Sounds like a similar project to mine. My boat is a 18.5 ft runabout, I paid $600 for it. Engine ran, drive was good, but both needed maintenance. Structure and interior of the boat were toast. I replaced transom / stringers / deck, new upholstery, and new dash. Spruced up all the little stuff. I'm probably into it about $10k total. Just so you can compare yours to mine.
Figure on using 3-4 sheets of 3/4" and 3-4 sheets of 1/2" ACX plywood. About 35 yards of 1708, about 20 yards of 1.5oz CSM, 25-30 gallons of resin, a few gallons of gelcoat, a few gallons of foam, a bunch of fillers, and lots of consumables. It adds up quick.