Unless it's an "Eddie Lawson Replica" it's not worth 500 bucks with a stuffed gearbox mate, Kawasaki parts are expensive and hard to find, and if it needs new cosmetic parts (sidecovers, badges, seatcover etc) they're not cheap either. Bikes are cheap in the US and you can do better.
I just bought a 1980 Suzuki GS1000 with full Yoshimura top end, Koni shocks etc, for $450.00 here, it sounds great on paper but it's as rough as guts, it was a "one owner" bike, but has sat under a tarp for 5 years due to a messy divorce, and will take a lot of work to bring it back.
I'm gonna swap the Yoshimura engine with the one in my "Wes Cooley Replica" (the mortal enemy of the "Eddie Lawson Replica", ha ha!) and clean up the rest and "flip it". Hopefully it'll all work out, but like your Kawasaki, it's a gamble! Cheers, Terry.