Dont know if this has been suggested before, but how about an "Introductory Level" 3 month Rook membership? (Available to a pawn upgrading for the first time only) with the benefits of a Rook - i.e. number of games/tournaments etc but without the creation of a Fellowship facility (incase they dont renew).

A smaller price (and time period) may tempt would-be pawns and once they get the benefits and see how good the site is, any subsequent renewal should be a minimum 6 months as usual....? It wouldnt cost the site any loss of revenue but potentially gives an affordable taster to those who dont want to commit to a full 6 months....