Cabinas Casa Verde is a very nice place. I haven't stayed there myself but I visited there, had breakfast there, toured the grounds and saw one of the rooms when I visited with Luck4unme when he was staying there with his novia. However, you should know you have to pay cash to get the rates below $50 (or take one of their more basic rooms w/shared bath and no TV or fridge).
I stayed at the Cabinas Guarana
http://www.hotelguarana.com. It is right down the street from the Casa Verde (ie similarly well located just 1 blk off the main drag). The Guarana didn't have any swimming pool and the room didn't have any TV or fridge, but it did have a private bathroom and a in-room safe and was otherwise similar in size and quality to what I saw at the Case Verde. And its low season single room cash price was just $25 compared to the $48 low season single room cash price at the Casa Verde. It was worth it to me to shave a little off the cost of my trip since I didn't care about the pool and didn't mind not having a TV for a night or 2 as long as I had my wireless internet and laptop loaded with movies to watch. However, the rates at Guarana go up much more during the high season than they do at Casa Verde so the price differential probably wouldn't seem so great for a couple visiting during the high season.
As for TripAdvisor, for whatever its worth, the #1 ranked hotel on TA (out of 30) is a place called Banana Azul but they're way over $50 and far outside of town (heading north). La Costa de Papito is the #2 ranked hotel but they're located about 1 mile outside of town to the south. Cabinas Guarana is a very respectable #3 on the list, is just 1 block off the main drag downtown and is extremely affordable (hence why I picked it).
Somewhat surprising to me, Casa Verde comes out only at #13, still semi-decent but putting it right behind Kaya's Place, which some of you may remember as a CRT VIP sponsor with its own share of mixed reviews. The last 2 reviews for Casa Verde are titled: “Would not stay there again†and “Bugs in the Bed and the "So What" Attitudeâ€. Personally, I didn't see those problems in my own brief inspection of the place and the reviews of people I KNOW have all been very good, but again I haven't stayed there myself. Apparently, this is a case of YMMV.
For me, Guarana had the best combination of good reviews, low cost and good location. IF you don't need all the extras like a pool. OTOH, if you don't mind paying a little more for the extras then go with Casa Verde and then add your own review.