Most brew shops mill fairly coarsely to prevent "stuck sparges." A 0.045-0.050" gap seems to be some standard there.
Maybe good for micro breweries and 3-vessel fly-sparge homebrewers. But the opposite of what you want for BIAB, which is rather fine for quicker and better extraction.
Only one way to find out what your shop does... Some will mill finer upon asking, some even do a special "BIAB crush."
For example, MoreBeer has been pathetic with their crush lately. No customization either with the bigger outfits.
There are threads and pictures posted of what a good crush looks like, also for BIAB.
Some shops will mill it twice, but it's still not anywhere as good as running once at the correct gap. (~0.025") little thinner than a regular credit card (~0.034").
The bigger problem with a too wide a gap is when you include small kernel grain, such as wheat or rye. There can be a severe lack of the wheat or rye contribution in the resulting beer.
You can make up the difference in extraction due to a coarse grist by adding a pound (or 2) of extra base malt and chalk up the loss.
Or mill your own as finely as you want. If you brew a lot, buying (base) grain by the sack instead of pounds, will save you over the long run.
A $25 Corona-knock off corn mill is as cheap as it gets and works well when adjusted for the fineness you want. If you're on a budget or don't brew as much this may well be your best ticket. The bag in BIAB is very fine and a good filter; the crush is not critical for that to work well.
A 2-roller mill will run $100-160. Or more. You can sometimes find used ones.
Power milling:
You could use a drill for either, as the hand crank becomes old fast.
Corona type mills are low demanding, pretty much any drill will do the job. Higher speeds are no issue.
For 2- or 3-roller mills, many drills won't "like" the mill-load presented, they either run the mill too fast, or groan heavily at lower speeds. A $$$ (DeWalt) portable drill may even get damaged by the heavy load and torque required.
A $60 (or less with the right coupon) Harbor Freight Heavy Duty Low Speed drill fills the ticket nicely. This is their current model, 0-600 rpm. Very high torque, it can probably break your wrist if you don't let go if it binds up!
https://www.harborfreight.com/12-in-Heavy-Duty-Low-Speed-Spade-Handle-DrillMixer-56179.html
Look around to see how deep the rabbit hole goes... there are some real beauties out there. Mine is not one of them, but is pragmatic.
For inspiration
My Monster Mill (MM2) with the older model HF Heavy Duty Low Speed drill:
![Craft A Brew - Safale S-04 Dry Yeast - Fermentis - English Ale Dry Yeast - For English and American Ales and Hard Apple Ciders - Ingredients for Home Brewing - Beer Making Supplies - [1 Pack]](https://m.media-amazon.com/images/I/41fVGNh6JfL._SL500_.jpg)
