I didn't see mileage listed but just based on age....
I'd suggest looking for a motor or wrecked bike.
Rebuild kit is $300 plus probably need a crank also. Block or heads could be damaged. Block would need to be checked and usually honed at a minimum. There are so many parts in an inline 4 that it drives up the labor costs.
All work yourself I'd estimate $1k minimum to repair engine. Shop cost easily double that or more.
Cycletrader shows these models $1900-2500+.
Not knowing what the other parts go for, parting out to fund replacement bike is always an option.