There are heating and cooling units similar to what you see in a hotel that can be low profile from the exterior. 

Divide those costs up over the remaining number of years of life for those major systems, and then add a bit more because while you may want the heating system to fail at the end of its life, Murphy's Law says it will fail years before then, so you better start saving.If you do go through the purchase, I would treat those capex dollars as spent dollars and put them aside in a separate account.  

@Austin Snow Sunnyside is getting very hot, feeling the heat bleed northward from Highlands.

I built a custom home last year in Northern NH for about $180/ft but that had a private well and septic with higher end finishes (quarts, custom cabinets, radiant heat, wood floors, ceramic tile, cathedral ceilings)

Once we get our finances under control (had to put a whole new heating system last fall, frozen pipes, and lead removal has set us back about $35K in the last year so always plan for the unexpected!!)

Your friend is correct in that the market has heated up enough to where all the low-hanging fruit has been plucked, at least as far as small multifamily properties go.

Paid $5000 in heat last year in one house that well insulated.

He reported about $5000 for HVAC (Heating, Ventilation and AC); Doesn't San Antonio get above 100 degrees? 

For example, things like a source of heat (furnace) in the wintertime, a working water heater, working plumbing/electrical systems, etc.

House also doesn't have operable A/C...so I don't see any extra motivation to get this done "in the near future" with sweltering AZ heat.