Affordable housing in Moab: who should pay for it?

At last night's Grand County Planning and Zoning meeting, the spectre of affordable housing looomed darkly over the various discussions. (Statewide housing prices are going nuts.) The Commission's been looking at revising the Multi-Family Residential Zone (MFR), which as it now reads will allow up to 20 dwellings per acre. That's incredibly dense. A revision would essentially add two more zones, where all of the MFR characteristics would be the same (permitting duplexes, apartments, etc.) but with lower densities - 8 per acre and 14 per acre. The catch is that if the County is to effectively address affordable housing, most likely it's within the MFR zone(s) that such housing would exist.

Therefore: should developers bear any of the burden to provide affordable housing, as a condition of developing within the MFR?