$650k would probably not build an AIRS site at all. I can about guarantee that Motorola would look at any of their existing sites and tell them "No" on putting an AIRS site there. So... New tower - $300k. Tower shelter - New $120k - Used $25k. Generator - $20k. Grounding for new site - $20k. AIRS site equipment - (Repeaters, UPS, Combiners, Tower Top amp, cabling) We'll say they are being conservative and do a 4 channel site: $400K. Microwave to the next closest AIRS site (Probably Trinity) $90k. Now there's $0 left for subscriber equipment . Even if they went with Kenwood subscriber equipment (which I would about guarantee most would), that's about $2200 per radio. I'm guessing they would need around 500-600 radios.
All of my numbers are from my experience building out with Motorola 12 yrs ago. I adjusted up a little based on today's economy and inflation. (and are likely too low)
You are absolutely right. Without going into too much detail, the original pricing I heard was around $1.3 Million for the new AIRS site. Not sure if this was RF/Microwave equipment alone, or also included a new tower and shelter. I believe there was some planned source of funding for subscriber equipment, but I don't remember what it was. Last I heard however, the cost estimates of the site alone had more than doubled.