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There are many questions to answer before anyone can give you a price for your new system. It's like calling a dealership and asking how much a new car is. They need more details, too.
Call a few HVAC contractors in your area and ask for bids to replace your system. Ask them what they recommend and why. Then compare apples to apples. A higher efficiency system will cost you more up front but will save you more on your energy bill. However, be warned that some of the super high efficiency systems don't typically pay off in savings due to their higher parts and service costs down the road.
Be leary of contractors who quote you prices over the phone or internet without looking at your home. They may be either inexperienced or will hit you with higher costs once on site due to things they didn't plan for and easily could have if they had just looked at the job in advance. Many of the big box stores do this with their installation services for all kinds of things.
Todd's Home Services