Value

The exhaust repair is fairly low cost, unless it's a catalytic converter. A muffler is around 100 to 150, depending. You can always patch a tailpipe with a kit, not the best repair method but dirt cheap. AC repairs can be expensive, depending on the part needed. There's not much of a blue book value for a high mileage Focus. If you can't perform basic maintenance yourself, or for that matter major repairs (that this is likely going to need) then I would not buy it, it'll cost you more in the long run. If you are on a budget and don't have repair experience or tools, look into leasing an economy car with a low down payment.