Under $30 with A/C could be a problem, however in SJ as long as you have a good fan and ventilation you don't really need A/C even if you're generating some of your own with a chica.
I've stayed a number of times at the Doral Hotel (
www.hoteldoralcr.com/). The single room rate there is $30/nt INCLUDING tax ($2 more with breakfast). Their website only mentions fans but I seem to recall their having A/C units in their interior rooms when I've stayed there before. More recently, I've gone for their outside rooms on the 4th floor south side. Those rooms only have fans but they get such good ventilation, you barely need even that and they have a stunning view of the mountains to the south. I haven't stayed at the Park, but I checked them out and feel the rooms at the Doral are MUCH nicer (certainly nice enough to bring a chica back to) and also are much more airy. Also, I don't recall what amenities they have at the Park, but the Doral has wireless internet, cable TV with many english language channels and there is plenty of hot water in the showers. There is a chica fee. I forget what it is but know for sure it isn't anything more than $6. They are located about 2 blocks beyond the Park Hotel on the Avenida 4 Pedestrian Way (2 blocks south of the Central Market). The area is not great at night but I wouldn't call it "ghetto". I've even walked short distances around it after dark (quickly and with regular glances all around me

) probably not highly recommended but always without incident. Its certainly safe enough to walk to the corner and flag down a cab.
Beyond the Doral, there are some other places under $30/nt mentioned on this board.
The Nuevo Johnson (
http://www.hotelnuevojohnson.com) is or was only $10/nt. The website actually says $15/pp, but they charged me $10/nt in July and $12/nt last month. Whatever the rate, it is a cheap place to stay if you just need a place to park your bones before catching an early bus in the morning, but it is not exactly a cheery environment. I suppose you could bring a chica back there and I doubt there's a chica fee (unless she stays all night), but I've never taken one there. The rooms are decent sized and fairly clean, the beds comfortable, door locks and other security adequate, all rooms have a private bath and a fan if you ask for one, and there is even a pool table you can use on the first floor. But other than that, the place is pretty dreary and very stuffy. The TV's barely gets a few fuzzy spanish language channels. If there is any hot water in the shower it runs out pretty fast. Even without a chica fee it is not a place I'd feel proud to take a chica back to or feel that comfortable with her once we started getting sweaty. It is located a half a block south of the Market on Calle 8. Just 1.5 blocks north of the Doral, but IMHO being closer to the Market and Bus Station areas and away from the patrolled Pedestrian Way a little dicier feel to the area late at night.
There are actually lots of places like the Nuevo Johnson, probably with similar rates and similar quality. I'll stay in places like that, but I'm guessing most of you would not, even to save a few bucks. Better for you to stick closer to the $30/nt price point to get the better quality even if that doesn't include A/C.
I've also stayed at the Hostel Marruecos (
http://hostelmarruecos.com) in one of their better rooms (with private bath). The rate I paid with CRT discount was $28/nt including tax. The room did not have A/C but again it was more than cool enough once they brought in a fan (had to turn it down). The place had many amenities such as wireless internet, cable TV, an electronic room safe (that did not work) and a gorgeous glass enclosed shower in the room (for better chica viewing). There is no chica fee and in fact the place also serves as an MP during the day with several chicas lounging around the lobby, but rarely any that were at all hot looking. That is all the good part. The bad part is that the maid service (or any service) is non-existant, cleanliness is shall we say highly questionable and the door locks and security was not overly reassuring given the fact that strange Johns and Putas were coming and going throughout the day. The location is much closer to the Gulch and even closer to several other MP's, but I'd rate the area safety as poor or poorer than the Park/Doral/Johnson area. Overall, I wouldn't stay there again and would take the Doral over it even with the greater distance and chica fees. But that's me, YMMV. You can see my full review on this place elsewhere in this section.
There are some other places that I haven't stayed but seem fairly nice and cost around $30/nt. However, I'm not sure how chica friendly they are. Those include the Aranjuez (
http://www.hotelaranjuez.com) which is located a few blocks beyond the Amistad. Their rates start at $30/nt including tax and breakfast. I don't know what they're chica fee is or if they even allow chica visitors, but if not you might still be able to register her as a fellow guest and pay the double room rate which is $10 more.
Another cheap but very nice looking little place is the Pensión de la Cuesta (
http://www.pensiondelacuesta.com). It is located just 2 blocks past the HDR going towards the Parque Nacional and Museum. A possibly deal breaker for many of you is that the rooms have shared bathrooms. But the rates are only $22/nt with additional discounts for paying cash or weeklong stays. The other dealbreaker is that I don't know if it is chica friendly, but again you could probably still register your chica visitor as a guest and pay the double rate which is $31/nt. Other members have stayed at each of these places and could better tell you how well they work with chicas, just do a search.
BTW, I've seen plenty of places in CR over $30/nt that had bugs. The cheaper places I've stayed at, for the most part, may not have been fancy but they were at least clean (or I wouldn't stay there). And if they were clean they didn't have any more roaches than anywhere else.