Ok - the way I understand it - for someone to sell an NFA item to another person, it first must go thru an FFL before it can be transferred to you. The ATF is going to charge the FFL the 200.00 for the transfer to them and the FFL is going to charge to do the paperwork so either the seller or the buyer will have to foot that bill. The seller will probably add that to the price of the suppressor if he has to cover it. Then you will have to pay the 200.00 transfer fee plus any FFL charge for the paperwork to transfer the suppressor to you - unless you want the FFL to sit on it till the first of the year.
IMHO, unless you can get it for virtually nothing, it isn't worth it as the savings over a new one will be nil.