I looked for a piston for my 00 GPGT when I grenaded the original motor. Best I could find was $225. This doesn't account for the machine work to the rest of the motor to make it survive. Replaced the entire motor with one that had 150K on it and still going at 317K. Don't waste your money on trying to save this one. Just get a long block or complete motor from the JY and go from there.
You can rent an engine hoist for a weekend and still come out way ahead.