We have some shops here for resurfacing (with 5000 Euro machines) which charge 3-5 Euros per disc. Luckily in one of the shops I know the owner pretty well so I only pay 1-2 euro per disc.
The experiences I made over the last years.
Ps2, Gc(with adapter), Xbox, 360 - look nearly perfect after resurfacing
Ps1 - only do those if they look really bad as you will always see resurfacing marks on the black surface
Older Cd based media - mixed results - some look prefect, some not
Generally a real good machine makes discs really nice looking, but still some scratches are unrepairable if too deep or punctuated.
If you are really anal and hold them against direct light from the sun or a bulb you will see the resurfacing waves a tiny bit.