The price is ok, I paid like 800ish to have a large strip of rust repaired on the to of my windshield frame. That involved pretty much the same as youre describing.

However I agree with y33. I would try some silicon sealant on those areas. IIRC the pillar usually is not what leaks. I would try pulling the carpet back to expose metal and put some talc or baby powder in a thin coat around the areas you suspect of leakimg. Then when it rains you wil have a clear indication of the path the water takes to get in