Our house is an older (1920's) style and the upstairs does not heat or cool adequately, so I thought about having a second unit installed upstairs. I've had a couple of quotes for around 6-7k to install a new unit and one contractor told me he was 100% sure he could replace my ac a-coil (which is pretty old) and compressor and the upstairs would be fine. He's saying that because it's old, it's probably clogged up with dirt etc. and is blocking a lot of the flow from my blower which should go upstairs.
My question is, does this sound like a normal problem, and would 2400 be too much to pay for someone to replace the ac-coil, compressor, and balance the system? Also, would 6-7k be too much to pay for someone to put a new unit in the attic for upstairs use only? My upstairs is roughly 24'-30'.