[billybek]

30 years of service from the old Trane unit!
Unlikely that will happen again....

I would do some serious research as to getting the most effective/efficient unit installed. I imagine you run your a/c down there a lot more than you run heat. Saving $50-80 per month on your electric bill will make the bitter pill of first cost much easier to swallow.

The cheapest install cost will net you something that Wayne has going on in his HVAC thread.
Re-sizing ductwork for airflow and seam sealing all the connections you can see makes a huge difference as does duct insulation where it is accessible to install.

Sheet metal is actually pretty inexpensive but the cost to install can be pricey. Beware of the installers that tell you that everything is great and flip in an air handler and condensing unit and give you a tail light warranty.

Usually sad install stories begin with these words. "I have found a guy that will do the job for way less than any of the other companies I have quotes from."
Walmart pricing? Expect cheap crap.

Going dual fuel is a great idea IMO.