Is airbath + air gun reflow appropriate for low-volume commercial production?
Depends on who's paying the guy who's doing it, what he'd be doing if he weren't hand-assembling, and what the boards look like.  As a number for comparison, my US domestic assembly experiences seem to come in at around 6.5 cents per pad (maybe a bit more at low volume), plus NRE's. 

Also depends on what your goals are for the assembly.  Do you need it done, or do you need it done inexpensively?  At less than 100/year, I'd assume the price of the PCB has not much to do with your business model, but I could be wrong.  If this is the case, I think the assembly method you describe, when carried out by an experienced assembler, and followed by good QC testing, is an OK approach.