I had a new EFM oil hot air furnace installed for $2400. There Are alot of variables, but instead of throwing $300 away on inspections, have a trusted Heating and Air conditioning installer accompany you to look at the house again. I've looked the same house more than once before deciding if I wanted to put an offer on it. The realtor usually makes @ 7% of the selling price of the house, so make them earn their commission. Tell them you want to look at it again, before deciding. Remember, the realtor works for the seller, NOT the buyer.