Well you know the old and tired cliche; "20 year old hull is only worth what someone will pay".
Still, the NADA guide will give you a fair idea where to start and backup to an offer you may make.
Also, does it come with a trailer and if so what shape is it in? The gelcoat condition will give you a good idea of its past life and care. These Genmar era hulls seem to be pretty sturdy and we've seen very little rebuilds on them. Mostly cosmetic and power. Wood in the deck, under the gunnels and cabin core but everything else was composite and pretty well sealed up. Still, ya never know what might have happened on a Friday afternoon at the plant and material ran out.
Hull wise, unless someone ran into a piling and holed the hull, you should be fine structurally.
Good luck.
