Okay -
One of my best friends is getting married and we're going on a 7 day bachelor party to Costa Rica. There's 20 of us going, we're all in our mid to late 20's, and we love to party heavily.
So, some questions:
What are the best hotels/casinos in San Jose?
Any hotel where I'm not staying.

Twenty 20-somethings on a bachelor party...potential for disaster, bad interaction with the cops, I smell disaster!
Regardless of where you stay, you might want to see if you can get a group rate with that many guys. Presumably, you'll be bunking no more than 2 to a room? This means you might actually qualify for a free room or a big discount. That's the good news.
In my limited experience but extensive research, there are some hotels which simply won't tolerate juvenile, uncultured or drunken behavior times 20... but YMMV
The Europa isn't the best, but at your price range and considering their discount policy for groups, you might like it. The Del Rey of course is accustomed to handling the needs of bad boys on the prowl, and with the BM right in the building, it's a 24/7 smorgasbord of sex. It's right in the belly of the beast, with numerous casinos, bars, and even strip clubs (gasp!) within easy walking distance.
I would avoid the Sportsmen's Lodge. Please.
(just kidding... it's awesome, but it may be a bit far from the Gulch for your convenience). Contact Bill or Ray and tell them your plans; they may be able to accomodate you, and it's a great hotel.
What are the best hotels/casinos in Jaco?
No idea. I don't surf, I don't much like the beach...
We'd like to spend between $50-$75US per night, but if a place is really awesome we'll go higher.
Uh, define "awesome." What do you want for amenities? A smokin' pool where you can babe-watch? A lively casino where you can play like high rollers? Hot and cold running women? Be more specific. If you're bunking two to a room, your price range can get you some top-shelf accomodations in Costa Rica, depending on what you need to be comfortable and entertained. Even going one guy per room, you'll be able to find something very decent. Don't forget that hotels have to charge an additional 16.39% tax, and the prices shown on websites etc. do not include this tax.
I'd say do the HDR (Hotel Del Rey) and live large. No pool, but what the hell? It's too cold in San Jose to really enjoy an outdoor pool anyway.
You might, with a little advance planning be able to get an entire floor, which you can make your own party central!
Another CRT favorite is The Presidente which I would classify as "awesome," with a rooftop jacuzzi and its chica-friendly policy. Plus, it's less than a two-block walk to the Blue Marlin and has a pretty good restaurant, a casino and a terrific new sports bar.
Be careful what you book, as many hotels have a no-female-guest (i.e. no hookers) policy. Remember, San Jose is not a whorehouse; it's a city where most of the population are very conservative and proud of their country; make sure the hotel is friendly to the kind of partying you have in mind. Hotels that I know are chica-friendly include the aforementioned Del Rey and Presidente, the Sportsmen's Lodge, the Hotel gran Via, the Hotel-Casino Morazan, the Europa and if you're cool and can behave yourselves when you have to, the Amon Plaza. There are certainly many others; some charge a fee for bringing a female guest to your room, some do not.
Any advise is much appreciated - we've got to send our boy off w/ a bang!
Eric, I wish i was 20-something again. I know you and your crew will have a blast.
Please, please, please... Do your homework by reading everything you can on this web site. Numerous guys have already done the hard research for you, so all you need to do is some fun reading. Join the VIP if you haven't already, because the discounts are great, you'll have another level of access to information, and you'll be supporting the best info source on playing for pay in Costa Rica...