Check with your local and state for tax credits as well. We got a new system a year ago.
We ended up qualifying for a state program here in NJ, details were found on the NJNG website. (NJ natural gas). It got us new high efficient HVAC, new hot water heater, and they installed it all differently to have the house now energy star certified. (furnace no longer vents thru the roof). The also put insulation up in the attic and reinstalled the dryer vent system. In all, $15,000 worth of work, for $10,000. The $5,000 balance is a grant. The $10,000 is repaid monthly, INTEREST FREE. So it costs us about $80-85 a month.
And here is the VERY best part. House is more comfortable, temperature is more consistent in the house. And our bills are considerably LESS. The AC bill was 1/2 as much as before.
Good luck!