Cost of New Gas Furnace

Just had the yearly tune-up/check on the gas furnace (w/forced air) and was told that it needs to be replaced. I’m waiting for the plumber to get back to me with an estimate for a high efficiency Carrier and was wondering what to expect. It’s a two-family attached brick house (approximately 2300 sq ft not including the basement).

Also wondering how much I will save on my heating bills with a new furnace. The current one has to be at least 30 years old.

Thanks.