You should just call the exchange you want to trade on. When I left in 1990, the min. capital requirement on the CBOE was 50k. Also had a seat on the Philadelphia and Pacific exchanges, but I don't recall what the min. Cap. Req. was there...probably the same, but that's a guess. I am sure a lot has changed in the intervening years. But you need to talk to the membership department of whatever exchange you are interested in trading.
Of course, capital requirement is only one part of what you need. Cost of leasing a seat, enough of a cushion to live on (don't count on an immediate income), etc.
Exchange membership department will help you out a lot. But even more than that, I found that the membership department of the clearing firm I used (First Options) was EXTREMELY helpful in giving guidance in virtually every way you can think of .... certainly in more ways than I would have thought to even have asked about. They saved me unimaginable time, effort and money in bypassing so much I could have wasted in trial and error. They really made life easy for me. I would have been lost without them since I started a new company from scratch. Never could have done it without their very capable, very friendly, and very free help. Maybe I just was lucky and had a good person as my contact, but really, it's their job to get clients, and a client is what you will be to your clearing firm.
Good luck,
Rs8.5