Got a good idea today:
Build base workshop / merchant stall.
"Rent workshop/stall to instert-race-here"
Costs 1 trade permit thingy from a caravan.
Turns the workshop into the specific workshop you wanted. (Merchant stall empty into Gnome Merchant for example)
Also produces 500 gold coins.
After 1 year (or a similar time) workshop returns to empty state.
This means you have to invite caravans, trade for a race specific item, use it to "rent out a building", which gives you money, and you can trade with these guys for a year. You can "prolong contract" for another of the race specific items you got from caravans, add another year for each time you do this, also creating more coins for you.