hey dave,
there's a fair few H3's floating around at the mo, with plenbty of satisfied owners. They're a really good boat.
I've got a 245 at home and am paddling a 255 out here (yeah, yeah, yeah, fat bastard and all that) and i love the boat.
The 255 wqould be way too big for what you need. 245 could be a good size for ya. Might be a squeeze in the 235. Check out the pyranha website for details on the weight ranges on the different sizes.
800 sounds like a good price if it's in good nick. It may only have 4 weeks use, but they could be 4 pretty intensive weeks, especially in norway