You can buy brand new slot mags for 129 to 160 bucks a wheel depending on the size. Id be surprised if you could find someone to weld, machine, and re-drill a wheel for less than that.
idk not into slots that much but some the older ones be worth it,the more common ones probably not! been years but the big truck wheel was way less than a used common verity aluminum budd truck wheel at the time,...said it can,..not that it should.