Yeah, every provider is different, but you can group them into 3 main kinds of party...
1. Swingers places which charge a small admission fee like £20-30, but hard to get invited as a single male. Once in, the ladies call the shots, so you need to get lucky to get laid, no guarantees. The quality of female is very variable, but you're likely going to have to be young & fit to get with a young & fit swinger a la Killing Kittens.
2. Budget Parties where you're guaranteed action as the girls are paid to attend. They're cheap, typically £60-£80 because either the quality (the looks of the ladies) is lower and/or the m/f ratio is high, maybe 4-6 or more guys to 1 girl. LSAP, LAPC & Pams in London and R3tro, Greedy Girls & Private Club in the Midlands are names that spring to mind.
3. Premium parties, the ratio is lower, typically 2:1, the quality is better with younger, more attractive girls, but price is generally £100-plus...Phoenix Club is £160 for new members. TLC & Fuck Club are trying to bridge the gap with premium girls at higher ratios. There's a new party in Cambridge that's £220, so they're really pushing the envelope on price. Le Jeu in Peterborough is even higher, not really a party, but a series of 1-2-1 experiences.
Do a search for any of the names on here and you'll find out more.