I'm a member on a number of forums covering multiple topics and one of the really depressing facts is that many of them are being purchased by big companies like VerticalScope who take over and start pumping the site full of advertising. You can pay to avoid the advertising, but there are other changes that happen as well, none of which are positive.
To avoid that, I'm happy to pay $25 a year, and be able to sell something now and then as a bonus.
Current eBay fees for most things are 13.25% up to $7,500 final value, 2.35% for anything above $7,500 and a $0.30 listing fee per order/sale. I just round up and use 14% to estimate. The fees are on both the cost of the item, and the shipping, but not on any tax. Selling one item on eBay for $200 would cost you slightly more than signing up for one year here.