I try to make decisions by elimination. AirWire gives you the most flexibility in chosing the decoders to use, you can basically use ANY DCC decoder with the CONVRTR, which is the configuration I recommend for AirWire. Some of your locos won't need the 6 amp unit, and can get the 2.5 amp unit, from $132 to $99 for the smaller unit. Then you add a DCC decoder with sound, for steam, the new WOW Sound unit is ok at $160.
But you say cost is a big issue, so I think I would eliminate AirWire, and if you are fine with the steam sounds the same on all the locos, the "new" Revolution is a deal that is hard to beat, lots of features and very inexpensive to boot. Also runs on 2.4 GHz, better technology and great range.
I like the inexpensive controllers from G Scale Graphics, but I think it would only save you money if you do not have sound. You could buy a cheap sound unit, but something like MyLocoSound is still $90. I think you can get the lowest price per loco, but you are sacrificing functionality and sound quality, in my opinion.
So, I think in your case, the Revolution is tops.