I had to drop $11K last March for an emergency furnace and A/C install. I can't complain as the furnace was 28 yrs. old. Certainly got my money's worth out of it.
If yours needs replacing, better to do it now before hard winter sets in and all the HVAC places are swamped with service calls. Having to do an emergency replacement is very stressful and not fun, believe me!
Check for rebates. I got a $1K rebate from my natural gas supplier in MA. Good luck!