They're not that expensive all things considered. I had an M1A, sold it. I now own 3 "M14's", 2 forged (LRB) and 1 billet machined from Smith Enterprise (Full auto).
An LRB will cost almost double what an M1A from Springfield runs. What you get is a receiver that's usually closer to USGI specifications, will often work more reliably with USGI parts, and have a longer service life. I have to say usually because I feel there is a lot of variance in the M1A's springfield puts out; some are better than others. To me, the extra features offered by the smaller M14 manufacturers are worth the extra cash, to many I can see how they would not be, especially if they have a "good" M1A. Unfortunately the M1A I used to own simply was not reliable and repeated trips back to springfield would not correct the failures to feed I was experiencing with that rifle.