Looking update home heating/cooling systems due to age

Yeah, we're lookin at the same thing before much longer, I'm afraid. Our outside A/C unit went like 6 or 7 years ago. The inside furnace still works, but we rarely run it because it drives the bill up so much. Present electric bill was over 200 up from the previous month's 179, so no doubt we need something more efficient. We have two small electric space heaters for winter and a medium size window unit for the hot months, but now that we're both retired and home all the time, we need something more. They're just so damned expensive. I've had several estimates over the past few months. One was almost 12K. For central heat and air in a 1600 sq ft double wide. LOL Like they actually thought I was gonna tell um to jump on it. Lowest one was about 4800. We'll get it figured out somehow. lol