A nice, complete #1 or#2 tiller with gearbox (hard to tell from pic) usually runs in the $300+ range. Rear lift setup roughly $100+. Nice deck $100+. Cub Cadet 1450, priceless.............and free considering attachments...........
All kidding aside, that's a good deal. Especially if you keep the tiller and sell the tractor and deck. If you figure out the dying problem and it's an easy fix, you could keep the tiller with rear lift and sell the tractor for pretty much the $500 you paid for everything.
BTW, we wanna see some more pics of this thing in your garage.