We have both enjoyed sailing when we've done it, albeit a limited experience and strictly pleasure vs. pleasure/transport. When I spent a week and a half on the Lady Maryland, she was a fully functional schooner, but we did have a few times when we ran the diesels to meet the schedule.
On the fuel being the cheapest thing you buy for the boat, that's proven true so far. Yesterday I topped off the boat and it took 40 gallons, which means that's how much we burned last year for 6-8 times out on the lake. About $110 in the fuel at today's prices. In that same period, we've spent money either for the boat or to support boating on:
- new batteries
- air springs for the truck so it can tow the boat better
- life jackets
- coolers
- marine grease
- brake fluid for the surge brakes
- title/registration fees
- new cover
- new propeller on the way
- probably $150 in fuel in the truck to tow the boat back and forth to the lake
- LED lights for the cabin for better brightness and less heat
And on the list for this year:
- expecting to have to redo/upgrade the surge brakes on the trailer
- redo the cushions in the cuddy cabin
- redo the captain's chair (the vinyl is in pretty sorry shape)
And that all assumes that nothing breaks on it.
So far that's been about $1500 spent (not including purchase price), with fuel being around 6% of total cost.
The 310 isn't dissimilar in the sense that dry costs outweigh fuel costs, but on the 310 it's about 3:2 vs 15:1.
Obviously, the dynamic would be different if we were truly using this to travel at about 3 MPG. The other day it looked like I might have to go to Boston for work, so we were joking we could go down to the Ohio river, take it to the Mississippi, go to the Gulf, around Florida, and up to Boston. That'd probably take something around 1200 gallons one way.
What you are describing are the startup cost of a project boat.