Girls charge as much as they can get out of you. At HDR/BM, they ALL start at $100 or more for 1 hour. In Del Rey, they are all independents so they can charge whatever they want. This doesn't mean you have to pay any more than you want to. You negotatiate with them for price, time, and specific services. In my opinion, the average price would be $75/hr.
If you are staying at HDR, you can take them to your room very easily. The hotel charges you $10 for each "guest" you bring up. The length of time depends on what you negotiated and agreed to with the girl. If you agreed to $100 for 2 hours, there's your answer. Some girls will try to leave after you pop (30 minutes or less) even though you paid for 1 hour. Also, do not pay before you finish your business. It is smarter to pay after the hour is up. If you pay ahead of time, they may give you bad service (they already have the $) and may try to leave early (they already have the $).
If you are not staying at HDR, make sure your hotel allows "guests" and if they charge a "guest fee". Different hotels have different guest policies so learn them. Most hotels discussed here do not charge fee. You can take the girls to your room or to a short stay hotel.
There is no dress code. You can wear whatever you want. Most guys dress casual, jeans and a casual shirt. Some guys wear shorts and t-shirt. Very few guys dress up. I recommend jeans and a casual, you don't need to impress anybody.
FYI--Besides HDR/BM, there are a lot of massage parlors. The prices there are set (no negotiating). Zona Blue, New Fantasy, Idem, and Oasis are the most discussed here. Here's a good list:
https://costaricaticas.com/phpBB2/viewtopic.php?t=5209
Have fun and write a trip report when you get back home.