Your talking new HVAC (ductwork?)

I can have an entire system put in, including ductwork, for $5k or so, maybe a little less depending on the setup.

I assume this price does not include replacing duct work.

This is what causes the motors to break - they are just over worked.Furthermore, the electricity that it takes to run the fan exceeds the energy that you save from cooling the attic - again, regional differences may occur, but this is at least true in the south - see this study done in Florida:http://www.fsec.ucf.edu/en/publications/html/FSEC-GP-171-00/You do get benefit of reducing strain on the HVAC system and ductwork if it is in the attic, so even though you are spending more on electricity, reducing the temperature in your attic is important because this will increase the longevity of your HVAC system (if it is in the attic).So, the conclusion is that for energy savings, solar powered attic fans are superior.

Forced hot air required a furnace and ductwork.  

Minor wall damage.Here's my spitball repair cost estimates:Plumbing backs up in shower 300Entry Doors (2 doors) 1000Replace windows (9 windows) 3000Replace water heater 700Replace HVAC/Install Ducts 5000Replace Cabinets 1500Replace Countertops 500Replace Stove 300Encapsulate crawlspace 2000Replace flooring 1400Paint/Drywall repair 2000Total 17700I'm pretty confident in most of the costs here, but if anyone has any additional feedback on the cost of new HVAC duct installation and the crawlspace encapsulation I'd appreciate it.Sidebar: I'm thinking it would be better to encapsulate the crawlspace and then run the HVAC duct work through that area rather than through the attic. 

@Andre KeyThe commercial air scrubber linked in the previous post will be what you need- BUT, in addition, you will need to clean the A/C coil and probably replace carpet, duct work - cleaning won't help - I had a smoked house and we re-painted every surface/primed with kilz, replaced carpet and cleaned coil and ducts--- smell was improved, but not gone until we replaced ducts- The air scrubber is a great starting point with a new project - it will remove 90% of the smell before you even paint-Good luck

That is easier fixed then foundation issue, typically.I would get 3 quotes from other HVAC contractors. if there is furnace and duct work, we typically pay 1800 dollars for the air conditioning.

You still have to make sure that the ductwork is correct size and distributed right as well.

Vinyl floors, new carpet, paint, granite kitchen and baths, new water heater, brushed nickel throughout, roof maintenance, new water heater, AC ductwork