Yeah, I'm not sure what you mean by commissioning? Is this a topic/book they want written and have issued a 'call for authors' or some such? Or maybe just approached you/a single author about this? (if the single approach deal, I'd think they would be more forthcoming on the projections/pay)
That's a bit different, but also much the same as a traditional deal...but....the devil is in the details.
a few links:
"....Today, some publishers are experimenting with low or no advances. In exchange for low-five-figure advances, the boutique press McSweeney’s, founded by Eggers, shares profits with its authors 50-50, as does the new imprint Harper Studio, which offers sub-six-figure advances. ..."
and one more: http://www.rachellegardner.com/2012/...cal-advance-2/