Unless the shop has a long term relationship with you, I am surprised they gave you a quote at all. Installing a BB takes a couple of minutes, so you really haven't done much there. And if they have to remove it to double check your work, what if you got the wrong length spindle, etc., installing it could be a negative.

What about consumables, cables, housings, etc.?

And do you know for "sure" all these used parts are in proper working condition and are fully compatible with each other? And fit your bike? Possible can of worms for a shop. If I were bidding it, I would guess high, and I would prefer to see all of the parts and frame first.