Good morning,
Let me preface this by saying I'm a mechanical engineer by trade, so I may be a little better equipped to do this job myself than some, and it's not one I recommend the beginner home owner take on themselves.
As part of my larger addition/roof replacement project for this summer, I have to relocate the heating system in my house, since currently I have a package AC/Furnace sitting right where the addition will go. I priced out what it would cost to have a professional put a new furnace and AC unit in my pantry. $8500 was the best bid.
I priced the components out myself, and was able to find a HVAC contractor who would sell me the furnace and other parts, as well as do a final installation inspection and fill the AC system, and register the installtion so I could keep the warrantee. Sweet. I did the heat load calcs, and spec'd out a unit. I went with goodman brand. My research indicates they have no higher of a incidence of problems than anyone else, and they use the SAME internal components as the big guys, except the heat exchanger and a few other parts. Goodman also doesn't have to mark up the equipment costs to cover a advertising budget.
My final budget came in at $4100, including all permits from the city, etc to do it up legal. Luckly most of my ducting is in good shape and is sized correctly, so I can re-use that.
As of right now, I have the system components on hand, and have drawn up and placed the order for the sheetmetal parts I didn't feel like hand-fabbing. The only thing I haven't bought/don't know the final price of is the sheetmetal, and unless they really surprise me on that, I'll make my budget for sure!
I've attached a few pics for those who like to see such things, and I'll update this as I make progress!
-Nick