$200 sounds a bit excessive, though $20 I think is fair, filters out idiots who just waste your time... though I think it should be refundable, if renter backs out, they lose deposit, if landlord backs out they should return the deposit... otherwise it's wide open to scams, very easy to collect bunch of applications and collect few thousand bucks for free... you could even probably make more from applications than actually renting out the place...
