Doug,
Aside from zZona Blue, which is really fun and a fair value, especially with the CRT discount, I'd also recommend Bar Idem.
Bar Idem is incidentally located very close to an excellent panAsian restaurant called Tinjo, pronounced "teen-hoe."
Bar Idem opens at around 3:30 p.m., with many of the ladies showing up for work after 4:30 p.m. Cost is 19,000 colones/hour for a simple upstairs room, or 22,000 for the downstairs room, which is air conditioned and has its own private shower. The bar closes promptly at midnight, so it's important to make your choice and have your fun before then; the bar is closed on Sundays. Unlike other massage places, the routine at Idem is a bit different. Typically, one approaches the girls, who are all seated near the bar along the back wall. Find one who appeals to you, and invite her over for a little chit-chat. Buy her a drink, and if you like her, make the move.
Besides the Blue Marlin, there's a big nightclub just across the parking lot called Key Largo. They feature live bands, three bars, and yes...chicas. Do not ever pay cien ($100.00); the veteranos here tell me that one should be able to strike a great deal, perhaps less than sixty bucks for an hour. Read the many posts on here about mastering the interview; in fact, do a search using the term "interview," and you'll get links to great tips and strategies.
Also near the Blue Marlin/Hotel Del Rey are a number of bars, any of which might have your next love waiting for you. Look around!
Again, there's a lot to learn by Tuesday, but if you do some research, you'll be better prepared for the fun to come, and you'll be less likely to encounter disaster. Wish I could see your face when you enter the Blue Marlin for the first time.
P.S. B.Y.O. condoms.