El Ciego is right that your chances of getting a clear view of the volcano at that time of year will be very slim (especially considering recent lava flows have all been on the opposite side of the volcano from most of the area hotels). In fact, its not that great most times of the year. If you plan to go to Arenal primarily for that, you'll probably be disappointed. OTOH, the thermal springs that the others have mentioned have always been that primary appeal for me.
TabacOn is arguably the nicest spring in the area but it is also easily the most expensive. I've met many people who actually prefer the other springs because they feel Tabacon is just a little too plastic and touristy. For others it may seem strange to describe a place with such "natural" surroundings to be "plastic", but at times it can seem almost too polished. But the real killer for Tabacon has been its ridiculous price inflation. When I first went there 9 years ago it was only something like $17 per day to get in. Today, their rates START at $70 per person for just their EVENING pass (w/dinner, see
link). That still might be worth it to check it out at least once (in much the same way everyone should stay at the HDR ... ONCE. However, given the fact that you're on a budget AND paying for your chica as well as yourself, you'll probably find one of the other springs as nice or nearly so AND more affordable.
I'm not sure what the deal is with Baldi. Their rates may have recently gone through the roof too. According to their own website, their least expensive pass (again the evening pass with dinner) is now only $10 less than Tabacon. According to that 3rd party link that Chico provided first, their day pass with lunch or dinner is only $37.50/pp, but that may just be because the info on that site is stale and hasn't been updated to reflect recent price increases. I will say however that the site he posted (
http://www.arenal.net) has traditionally been one of the best sources for GENERAL info on the Arenal area (including listings for hotels).
Some other springs in that area to consider visiting instead or in addition to the one's listed thus far include:
1) Eco Termales Hot Springs - Sorry no known link other than Arenal.net. Prices used to be just $21/pp ($10 for ticos). Much smaller than the other hot springs with only 5 pools but they don't allow more than 100 people at a time vs the huge crowds that can sometimes mar the appeal of Tabacon.
2) Los Perdidos - One of the newer places (
http://www.thespringscostarica.com). $32/pp per day plus any meals according to Arenal.net but only $25/pp according to their own website.
3) Titoku Hot Springs - Another one of the new hot spring options. Titoku is associated with the Kioro Resort but located on a seperate property about 5 minutes away (right next to Baldi actually), so I'm not sure if this is the same hot spring that Chico was referring to (according to their website,
http://www.hotelarenalkioro.com, it seems they may actually have a 2nd hot springs at the resort itself). If Chico has been to both Titoku and Tabacon then I defer to his comparative assessment because I haven't had the chance to check this place out myself. However, it looks like the Titoku could be a very cool place to visit at night because of the colorful ambient lighting they use. It is also supposed to be more "intimate" than Tabacon. Oh yeah, their DAY rate is $52.32/pp and I believe that comes with some "chips" that you can use to purchase snacks or light meals (?).
4) Los Fuentes - The "Tico Hot Springs" across the street from Tabacon and owned and managed by the same people. Not really worth mentioning in the same breath as the other places, but still very nice at MUCH lower prices ($10/per gringo and $3?/per tica or free w/Tabacon admission). Doesn't have all the facilities or lush landscaping of its sister springs across the street, but still probably nice enough to please a tica. Going by myself I'd probably spring for one of the fancier places, at least initially, but if you've already tried one or more of the other places and want to do another spring without having to pay another large entry fee, this could be your place
Here is a link (a little out of date) that does a good comparison of the 3 "original" places (Tabacon, Baldi, Eco)
http://www.northerncostarica.com/hot-springs.html
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What about BUDGET but nice places to stay? I have to say that if Chico was suggesting the Kioro Resort as a BUDGET place to stay, then I don't know what planet he is on. It may be worthwhile for someone on a budget to VISIT their hot springs for the DAY, but their rates to STAY overnight are as high or even higher than staying at Tabacon (ie $250/nt and up). Kioro's standard rate actually starts at $310/nt but they're offering a "discounted" rate of $248/nt. According to one CRTer (I forget who), discounted rates may be available at Tabacon too during their non-peak season IF you know enough to ask. Unfortunately, discounts may bring them out of the stratosphere, but I doubt you'd be able to get a rate their that would qualify as "budget".
What exactly IS your budget? Also, it would be helpful to know how you're planning to get there. If you don't have a car, you might prefer to stay closer to town. Fortuna may not have any real "scene" as El Ciego said but, unless he has been there recently, I think he might be surprised how much more things have picked up. Being closer to town will also be more convenient to inexpensive dining options other than just your hotel's. The less expensive hotels tend to be closer to town as well, however, like MA, the Arenal area is not exactly a place where you will find a lot of real value options and I think you'll find that hotel rates tend to be fairly inflated for what you'll get.
In addition to the Arenal.net site, you might want to follow this link to TA reviews:
TA Arenal Budget Hotel Reviews
http://www.hotelvistadelcerro.com/ is one budget place in particular that gets decent reviews and is just $40/nt
http://www.termalesdelbosque.com/english/index.htm also gets good reviews (particularly by another CRTer whose name I forget. It is actually some distance BEFORE you get to Fortuna and even further from the Volcano but its not like you'd be getting good views of the volcano in October anyway and this place will be more of the Tico experience your chica would be comfortable with rather than hanging out in such a heavily gringo touristy area like Arenal itself. Rates are a bit out of the budget range at $75/dbl/nt but is supposed to be a good value.