Yes and no, it depends.....
Entry fee is only 500 CZK in Prague while, depending on which time and which German FKK you go to, it varies from 35 to 70 EUR. On the other hand, you have free drinks, sometimes free buffet in German FKKs (some have free beers, some charge for beers, some don't allow beers....).
For going to the room, same thing. 1800 CZK for 30mn in Prague, and 2200 CZK for one hour. It's 50-60 EUR for 30mn in German FKKs, and can be same amount again, or only half of it, to extend it to one hour (depending on the FKK). Prague charges 500CZK per extra, some German FKKs don't charge for some extras, and a lot for some others (up to 50 EUR for CIM, 100 to 150 EUR for anal, etc...).
So FKK Prague can be more or less expensive than a German FKK, depending on which German FKK you're going to, what time of the day, whether you eat and drink a lot or not, how many girls you're taking, for how long, which extras you're fancy about...