Attic conversion, yes or not?

[Dale Crawford]

We bought an older duplex as a buy & hold. The attic has space has a stairway & room for about a 12x12 bedroom. I would guess I could get an extra $100/month rent by converting it. My contractor originally told me about $2000 for the work. Now we need to add a new motel style heating & air unit because of the way the HVAC is so now we're looking at $5000. At what point is the cost of the conversion prohibitive? Has anyone used any other options for heat/cooling?