The US hasn't made AP in 50BMG since WWII, its by far the most accurate of all. APIT has tracer compound to deal with and as it burns will cause the bullet to destabilize faster, that's why it would be my last choice. If you're worried about saving 30 rounds then buy Raufoss, it will cost 10 times APIT but will hold its value or increase in value.
The only other round to match its armor piercing abilities is a SLAP round, maybe buy half and half. As for SLAP, you'll need to be sure it will fit your chamber and to fire them take off the brake. If the shoe opens in the brake, nothing but bad will happen! Personally, just buy a bunch of components and save them as it will be cheap and you can always reload them.
Look at it like this, buy 100 new cases, if you load them light you can get at least 10 loadings or more. That means 1000 rounds of whatever projos you buy, so add primers and powder for 1000 rounds of ball, AP, API and APIT. Pretty good mix but first check your local ranges or laws on shooting and owning them. You might be better off with a different combo, YMMV.