I think we've spent maybe $300 for maintenance costs on the high efficiency system and that was on the AC side, not the heating side...refrigerant leak on the older outside unit that we did not replace when the new inside unit I referred to went in.
I agree with another poster that getting multiple quotes is a good idea. Also note that the same units are often sold under multiple names; the "well known" brand name having a higher cost than the identical unit under the actual manufacturer name, etc. The difference is sometimes a couple grand! Just like the home appliance industry only had a few manufacturers, so is the same with the HVAC industry at this point.
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The most expensive tool is the one you buy "cheaply" and often...