It depends on how good you are with restoration and mechanical work. $800 seems steep. The trailer may be worth abut $200 and the engine, if it runs about $300. The boat is probably $0, since it needs restoration. So maybe get yourself a deal at $400-500
Plan on replacing the stringers in addition to the floor. Overall, it is not a difficult restoration, because the boat itself is pretty simple.
Don't assume that the engine will work under load conditions, just because it 'works' (runs).
In addition to the structure/flooring, it looks like you will need to get seats for the boat. Plan on about $700 for the wood, fiberglass, resin and foam materials. Then whatever seating costs. Also plan on some $$$ for the engine.
Maybe $2K as a budget + the cost of the boat. (so about $2500)
Does the seller have clear title/registration for the boat? Have you checked the state regulations in your area to understand what you will need as proof of ownership to properly title/register the boat? (show stoppers if not)