Last I saw, $150 to $200 seems to be the going rate for Type 99's. They're pretty much all in a safe-to-shoot condition, even the last ditch ones. Postwar testing determined the Arisakas (both Type 38 and Type 99) were absurdly overbuilt. The only rifle P.O. Ackley couldn't blow up in destructive testing was a Type 38, with the Type 99 being the last to fail. When testing, he rechambered all the rifles for .30-06 and loaded them as hot as he could get them. Even the German Mausers failed before these things did.
Hornady makes 6.5 Jap and 7.7 Jap ammo. They use PRVI Partizan (PPU headstamp) cases. Reload the 7.7 ammo exactly like a British .303. Same bullets (.311) and same powder charge.
I have a Kokura Arsenal Type 99 that my grandfather brought back from Okinawa. It's an early-production model from approximately 1941, and still has intact antiaircraft sights. It's otherwise beat to hell, but a fine shooter. I did a lot of research into that rifle. For some reason they removed the firing pin before they let him ship it home. I managed to source the parts and got it working, and my grandfather finally got to shoot it before he passed away. I also purchased a bayonet for it at a gun show. Cost me $80, but it was a proper Kokura bayonet with hooked quillion.
Regarding last-ditch Arisakas, a guy at the gun show said it well: Some of them look like crap and shoot great, others look great and shoot like crap.
My grandfather in 2003, finally getting to shoot it after all those years:
The intact antiaircraft sights:
The bayonet I purchased for it: