Dieudonne Saive patented the basic mechanism in 1936. He was working on a good rifle when Uncle Adolf invaded in 1940, so upped tools, design and prototype and off to England. He engineered the SLEM in 7.9x57 while working at Enfield, went back to Belgium and put it into production as the SAFN-49. Seeing the writing on the wall as regards short cartridges, he immediately started redesigning it into th FAL.
Feodor Vasilyevich Tokarev swiped the design in 1938, modded it after tests into the SVT-40. Simonov, designer of the SKS, worked on Tokarev's team, later came out with his own 2 rifles: PTRS and SKS, both using similar mechanisms.
SAFN will run you a grand or better for a good one. Total producton was only 160,000, spread out in 8 contracts and 4 cartridges.
SVT-40 is a vastly-improved SVT-38. They are available round $400 right now, but that WILL go up.
SKS starts around $160 for a really nice one. Ammo is cheap but they tend NOT to be accurate.
PTRS, on the other hand, runs bout 3 grand and ammo is about $30 a shot. Just a TAD on the rich end of the scale.
FAL, of course, is no-no in this Free Country of ours. So is the Majority of M-14 production. There WERE a small number of Winchester M-14s built without the full-auto parts (VERY early Winchester production only) but they are about as common as lunar cheese: I have seen ONE exactly.
There are Chinese copies of the M-14 being made; it takes the same 7.62x51 cartridge, run bout 450 bucks, new. If it's the STYLE you like, the Yanks DID build the E-2 stock for th M-14: pistol-grip stock.
So there ARE several possibilities.
Stick round and we'll get them all hashed out somehow.
And welcome to the forum!