Temporary shops sound like a good idea. Maybe the longer you want the shop around the more it would cost up front.
I was just thinking:
Tier 1 ore shop: copper, tin
Tier 2 ore shop: dermite, silver
etc etc, same with wood and other materials that may be introduced.
But opening a shop would require you to have a shopground, i.e. a 16x16 and a 32x32 baseplate option for the shop, otherwise, no shop bots can be placed.
Placing a shop baseplate would cost around 300-400 gold, depending on what you want to sell, then placing the shop bot would cost another 200 gold or something like that.
Consider it as you please.