Does anyone know how much it costs to get the starter mounting block milled

 

Why are you doing this? Is there some sort of a Problem you're attempting to fix this way? Exactly what motor and trans do you have?

 

the starter always messes up after a month or so of being repaired after that a grinding noise is heard everytime i try to start it... i have an 87 trans am with a 400 engine(from the 70s) it used to have a 305 LG4 with the auto transmission that i still have on the car

 

Before machining the starter mounting pad, I'd suggest mounting a starter without the field winding, manually engage the pinion, and measure the angle and clearances. You may have one of those blocks that has holes drilled/tapped in the wrong location, or may actually need only to shim the starter.

Make sure you use a NEW pinion and starter nose with NO WEAR.

 

Also, are you using REAL starter bolts, not just some random ones out of your bolt collection?

 

Also, when you check the pinion tooth clearance, rotate the flywheel around to a few different spots to see if the clearance is the same all around. Sometimes the flywheel gear can be pretty far out of round (due to damage, warpage, whatever). If this is the case, it would be easy to think you are shimming the starter correctly when in fact it could end up too tight or too loose depending on where the flywheel was when you checked the gear tooth clearance.