Try this cheapo method:
1. Don't plan in advance. Watch Kayak or other flight discounters for a cheap fare, then jump on it.
1b. I have used F.F. miles twice now and have paid a total of $83.00 for two R/T flights from MSP to SJO.

I can do this because I run virtually everything I can through my F.F. rewards credit card (in my case, and AMEX Delta Sky Miles card). It's surprising how quickly the miles add up, and if you pay your bill in full and on time, you won't even pay interest on the charges.
2. I understand Mr. Black's desire to maintain a certain quality of living while in C.R., but if you can rough it a little bit, you can get killer hotel deals You can pay less than $39.00/night even in good, safe, clean and comfortable hotels. . Paying cash and showing your V.I.P. card at some hotels can get you a comfortable, basic room for $35.00/night close to the action.
3. Get your sex from "tico MP" girls, whether on-site or back at your hotel. Speaking a little Spanish will allow you to arrange a date outside the MP, and this can be done for as little as $30.00 with a quality chica.
4. Food: Take advantage of your hotel's free breakfast. Even the basic breakfast at the Castillo can be filling enough to carry you through to supper. When you make that Mas X Menos run, buy some crackers or tortillas, some cheese, ham etc. and eat lunch in your room. Buy fresh fruits/vegetables to eat from local merchants. Produce is amazingly cheap at the feria south of the Gulch and the market can be reached easily by local bus.
5. Hand wash your laundry. If it's just a five-day trip, you can easily hand launder underwear, socks and T-shirts in your hotel room.
6. Don't give to beggars. Don't give the chicas "trinkets."
7. Share taxis with others and split the cost. Learn to use the San Jose public buses. In fact, take a bus in from the airport (bus route #200B from just behind the parking garage opposite the exit from baggage claim/customs. Less than $1.30 to get into town. It can be a pleasant walk (daytime) from where the Alajuela/airport bus stops at Parque Mercedes to your hotel.
8. B.Y.O. condoms, motion lotion, etc.
9. Throttle back your drinking. Even in C.R., booze by the drink can really add up!
10. Avoid the casinos. Avoid the HDR/Sportsmen's/KL where the girls on average want a minimum of $70.00/lay.
11. Scam other CRT'ers for drinks and meals.

Just kidding...
Mr. Black, great post!