Yikes..
Like BDI has eluded to, if you check the recommended maintenance schedule on motocross bikes, I don't think 80% of us could afford to run them..
Pistons and rings according to the owners manual of my 2000 is inspect every 3 races and replace every 5 races.. how many hours is that 15-20 including practice?
There is a thread on the piston window mod by Stewart you could apply to another or overbore piston if need be.
There are several options at this point and maybe some of the other guys will chime in.
If you are considering re-plating, you may be able to go back to stock, however there is a limit to how much plating can be applied. Oversize, re-plate or oversize sleeve,
or stock dia. and sleeve.
Well, Things can only get better now!
Best of Luck...
Tuck\o/