Many of use here are using with Breathing Color's "GlamourII" or Clearstar's "Clearshield." They both cost around $80/gallon but if you buy in quantity it's a lot less.
I dilute GlamourII with about 45% water and spray it with an HVLP gun. I wind up using about 0.5 ounces per square foot to get a kind of satin finish using only the gloss version. So I get about 250 square feet per gallon, at very roughly $0.32 per square foot. If you are doing quantity you definitely want an HVLP gun since you get a much higher success ratio, and use much less paint than if you use a roller.
I did try some commercial water-based coatings. I didn't like the MinWax at all, especially since it did not spread well with a roller and probably could not be sprayed well. The best commercial coating I found was "Simple Success" from Woodworkers Supply. It rolled on extremely well, by far the easiest roller application of any coating I have ever tried. However, it contains some nasty chemicals and smells like it, you can't even buy the gallon size in states like California.