I have never heard of straightening a steel wheel (well, other than the pounding out of a bent wheel lip ... I am guilty of that).
I can't help but wonder if it would be cheaper in the long run to just replace the wheel or wheels with better ones, or pop out the centers and weld them to new "hoops".
it was a common practice back in 50s- 60s 70s quite few places did it.as thirty8 said $5.00 which at that time was cheaper than possibly $30 $40 new one.that was a time when you could buy a 50s-60s-70s wheel now 30-40 years later no where to buy one so send it for straightening.I am surprised there are places that still offer that service like most old school way's of service a dying art.