Yes. 500 members a month is realistic. Now you probably think wow that's 15000$ in the pocket! Wrong! Provided that you have all the gear and content already available, you'd have to pay:
Affiliates, Host. CCBILL fees, Models. Misc(overages, chargebacks, voids)


Then there is probably 30%-40% left of that money. Now that's if you manage everything yourself. i.e, design, programming, etc.