Yeah, you could use a Janni to get things brought across. That gets round Planar Binding's one task restriction.
In general creatures much more powerful than a human are going to want a better pay scale.
I'd be prepared to accept that they could also give a better reward.
An Azer is pretty much going to be the same as a human smith.
An Axiomite (with +18 craft) would cost more to get, but produce more/better items. Theoretically they'd cost more to run, as well, but as that's offset by the selling prices of items it wouldn't impact you.
Therefore a Smith defined as Axiomites would cost more to buy, but produce more per turn (probably a 'double smithy') I would think.
A deal with a Mercane is very clever, and would let you set up a much better trade route, albeit one only interested in magical items. Which, given all of you can craft, could payoff big-time.