Depends on the type of rifles and what you consider ďbuildingĒ?
A guy building guns from raw materials needs a lot more than the guy sticking a new barrel and plastic stock on a REM 700.
I bought my manual mill and lathe used with a bunch of tooling for $5000 if I recall correctly. Will have about $5000-$7500 in my cnc mill once itís complete. Have another $20k-$25k in various other machines and hand tools.
Iíd guess $7500-$10k would do the rem 700 rebareller a lot of good.