1. I have not seen T99 Arisakas in complete condition, let alone shootable, for under $100 in many years. Sub-$100 Mosin-Nagants are another story. There's a gun show in Springdale, AR, January 29-30. There will be Mosins there for probably $89-$99.
2.
No other cartridge is safe to shoot in a 7.7 Arisaka but the 7.7x58, which, incidentally, is not rimmed, nor even semi-rimmed like the 6.5x50.
3. I know of no source of 7.7x58 surplus ammo. If you know of any, please let me know and loan me your credit card!
4. 7.7x58 ammo is not too hard to find now. Norma makes it with a 174 gr bullet, but it's expensive (~$38/box). Hornady also makes it occasionally, more like ~$26/box. Vendors at gun shows frequently have it. But reloading is almost essential for 7.7 because the supply does sometimes dry up, and because it's not cheap anyway.
5. In addition to .303 British and 7.62x54R, the 7.65x53 Mauser uses the same bullet (
not cartridge).
6. I got a T99 in a trade at a show a while ago. It had an intact mum and appeared to be complete for a 7th Series Nagoya, except about an inch and a half of the front end of the stock had been shot or burned off. The metal was all there, though. I got it home and put a 7.7 round in the chamber. It rolled around loose and fell out. So I thought someone had rechambered it to .30-06; that's not an unusual modification. I put a .30-06 round in the chamber, and it went in too far! I began wondering if someone had rechambered and maybe rebored it to take the 8mm Swedish machine gun round! Anyway, I took it to a gunsmith, who made a chamber cast. Sure enough, someone had tried to rechamber it to .30-06, but used a drill, not a reamer. The chamber was ruined. The gunsmith had a T99 barrel, so I had him put it on and headspace it. His barrel was chrome-lined. Mine wasn't, as the chrome barrels were discontinued before Series 7. Since the rifle was now no longer "original," I also got a new stock from Numrich. Voila! A brand-new T99! So If you encounter a T99 (or a T38, for that matter), look out!