I've ordered an RMR 06 and it should arrive any day now. I'd like to have my Glock 17 milled for the RMR. I have one general question about the process: is it better to have the optic in front of or behind the rear sight, and why? 

On to the main question, where should I send it? I have been looking closely at Jaegerwerks and Primary Machine. Both are pretty similar in cost. I've seen a few recommendations for both in archive posts, but can't find a whole lot of info on them. Are there other "budget" companies I should consider with reasonable turn around times? I know the main place is ATEI, but I'm on a budget and I'd prefer to have it back sooner than one month. 

I just sent mine off to J and L Machining Works yesterday.  Their prices are really reasonable, and from what I have seen, their work is too notch.

You shouldn't put the word "Budget" and "Milling" in the same sentence.

Go with ATEI and it will be done right.

Primary Machine has a presence here and apparently does good work.

+1 

Doug at ATEi started this and the slide serration mods.  All others copy his work.

http://ateiguns.com/