I’m curious why he doesn’t think the 105-7000 crank and bottom bracket would work?
The nice thing about Shimano Hollowtech II is that you can mix and match left/right sides all day long (I have a 2018 4iiii left side powermeter crank mated to a 2005 Dura-Ace right side, zero problems).
And an 11 speed crank will work with a 10 speed chain.
So I can’t imagine why your LBS didn’t suggest a new bottom bracket and whatever Hollowtech II drive side fits your budget.