Having never attended a party, I'm probably not the best authority on this. I would be keen to attend a party providing the ratio of guys to girls is right, which in my opinion should be no more than 3:1, the thought of hanging around waiting ages for a "shot" with another 24 guys turns me right off. Some of the reports on the porn@thepartypalace thread stated that there was around 30 guys at some of them, that sounds like hell to me. What did you think?
In regard cost, depends on how long you'd want it to last. £100 per hour seems pretty reasonable in my opinion, maybe reducing to £150 for two hours. This also depends on the guy:girl ratio as well, don't get greedy, but if this is truly about fulfilling a prossie bucket list, then the cash side of it shouldn't be as important to you.
Bit of a balancing act in regard cost,ratio and quality. Who were the other girls you had in mind? Some of the girls who used to share the flat with you?
Edit: Re: the other girls attending, a yes/no answer on your former flatmates would suffice, Edinburgh punters will know who they are and don't what you being accused of touting...