HVAC and water heater is out of warranty

[Brendan Seals]

So, this 3 bed room, 900 square feet, home I am planning on buying HVAC and water heater is out of warranty. I believe the Hvac is 23 years old and the water heater is 15 or more (as I remembered). The seller wanted 74,000 for it and and I asked for 68000 on it and we came to 70,000. I am thinking that those items alone could cost 4,000 to 12,000 and plus there are other problems of repainting (there was a smoker that lived there) and other electrical modification I have too do. It all together cost up 13,000 15,000 to rehab it and be good for renting. So, it would I be wrong in going down 65,000? I would have to pull out a little more for the money to fix it. What would you recommend?