3-4 years ago you could get an SKS and case of ammo( 1440 crate) for CAN$500, these days. Now days prices for SKS range from $250 to $500 depending on year and model.
Options if you rebarrel, original bolt/extractor, same overall case length
1. .223 Winchester Super Short Magnum
2. .243 Winchester Super Short Magnum
3. .264-25 WSSM
4. .300 Olympic Super Short Magnum
5. .338 AR Short Magnum (ARSM™)
6. .358 BFG (1.625")
7. .458 B&M Super Short
8. .460 Alliance
9. .475 B&M Super Short
10. .50 B&M Super Short
11. .50 Liles
12. .500 Auto Max
13. .500 BAAR
If you also modify/rework or replace bolt/extractor there are 368 options. If there is another caliber you're considering ask and i'll check the list, 368 choices are to long to list.
The 7.62x39mm is doable if bolt /extractor modified below .25WSSM vs 7.62x39mm case dimension