There are escort sites for Costa Rica, never used any as it is quite easy to find girls in SJO, actually meet, talk and get a feel for them before pulling the trigger. I would guess it would be a bit more expensive to go through any listing site. I've seen ads for girls in CL and the prices are about what ******* want here is the states.
Keep in mind prostituion is legal in CR, pimping is not
In the TR section there is a guy who just used an escort site to make sure he had a girl on his first night that was be into a couple (he and his wife) you may try drooping him a PM if you are set about going this route to get the particulars.
Bill