Prices are negligible between stores, IME. You can get deals on some things at one one store and not the other but if you are really intent on being a jew you just need to compare prices between both to find the best price on a specific item and watch for the sales.

When buying lumber from either store always carry a pair of your own shears to cut metal banding they use to bundle the stacks. They hate to open a new bundle until an old one is gone but usually by the time 3/4 of a bundle has been picked through the stuff left is shitty quality and most employees will refuse to cut open a new bundle for you so just do it yourself.

Avoid buying items from the "convenience" displays( aka Impulse racks) these are usually located at end caps near registers or are stand alone displays. Go to the actual section or aisle for items as you can usually find better deals for more quantity for equal or less money on the shelf where the same item is offered by different manufacturers. I've seen blister packs for 5 of something sell for 3 times as much as what you would pay for bulk quantity of stuff like screws, bolts, nuts, tape, glues and adhesives at both stores. Its easy to get a decent deal on big materials and then get nickel and dimed to death on the supplemental materials you need to do the work.