It is difficult to comment on a price without any details. Can you supply the size of the condenser, the model number of the air handler, and a description of what duct work is being done?

It is difficult to make a fair judgement with such limited information. However considering the base price of a XLI20 plus the costs of installing ductwork I would say you are in the ball park for a reasonable price. Comparable quotes are the best way to keep contractors honest. Don't be afraid to let others know what quotes you have in place and see if they can beat it. (I would suggest giving the 1st contractor a 2nd opportunity to bid considering the time invested)