Sixgun, if you've already bought the Chinese gun, stop here, don't read any further. If not, let me offer another point of view. Friend of mine bought one of the early Norinco M1As when they first arrived here. It didn't look at all bad, fit and finish were not that far off what my Springfield M1As have.
Maybe 200-250 rounds of USGI mil surp, the face of the receiver was badly battered where the op rod hits it, the op rod cam surface was peened badly enough where it first hits the bolt roller that a pronounced raised sharp edge was created, the hammer wouldn't stay cocked if you let the bolt close on an empty magazine, and the aft faces of the locking lug recesses in the receiver were upsetting noticeably.
He stuck in his closet and bought a Springfield that he's been very happy with.
I own four varieties of Springfield M1As, from very early production to a customized "loaded". Two of them have upwards of 5,000 rounds on them each, the others have only 300 to maybe twice that. They're still in excellent shape.
You definitely can get the Chinese receiver re-heat treated, and just replace the other parts as and if they go bad to spread the pain in your wallet out over some time. But the prices of fixing the Chinese gun, on top of the $500.00 it costs you up front, are very likely to exceed what you can get a used, excellent condition Springfield for.
Example: Two months ago I bought the "Loaded" gun I mentioned for $800.00. It had a USGI fiberglass stock, heavy stainless steel "match" barrel, a box of USGI spare parts and the Springfield gas cylinder lock wrench and cleaning tools.
As it happens I like the fiberglass stock enough that I don't plan on changing it. I bought a few USGI mags (though the Chinese mags actually do seem to be OK in my experience with them) for about $40.00 apiece and I bet I still have less in it than you'll end up with in the Chinese gun.
The bit about whether the receiver or any of the other parts are forged or cast is totally irrelevant. The choice of alloy used, it's heat treatment and even the finishing are more important than whether it's forged or investment cast. The first two of them are FAR more important in terms of the strength of the part as well as how it will wear and hold up under the mechanical pounding of the action cycling.
How to get a Springfield M1A for that kind of price? The Internet, and patience. Get used to visiting gunbroker.com, auctionarms.com and gunsamerica.com as well as the equipment exchange pages of this board. Battlerifles, falfiles, sturmgewehr, subguns, snipercountry and jousters all have for sale pages too with the M1A's showing up frequently, though not so often at really great prices.
Good luck with it however you decide,
Pat