When I run numbers like this (''Back of a napkin calculations'') I over-estimate costs and under-estimate revenues. I use the very rough formula that when you take out a mortgage, you will pay back about 3 times the amount borrowed over a 30 year period. So if you borrow $500,000, you need to pay it back at the rate of $50,000 annually. Hopefully you can realize $25,000 from the farm lease and your charter members will put up a chunk of a down payment, so maybe you can reduce your mortgage payment that way. Still, you need to assume that you'll have to service debt to the tune of maybe $30,000 annually, probably more. Divide that by 100 club members, and you are at dues of $300. But you'll need to cover contingencies as well, insurance, maintenance, club house, sealing the runway.
For a well planned and well managed flying site with a nice clubhouse and a properly and safely laid out runway, I'd say that a $2,000 initiation fee and annual dues of $400 would be reasonable. However, that would put flying out of reach for MANY modelers. Cheaper than golf however (local country club here: initiation fee , $30,000, annual dues, $5,000).