Is it worth fixing my car?

The mechanic's quote looks scary. Let's see if it actually is.

Your gut says "that's too much to put into an old car." Maybe — but the gut doesn't do math. Repair-vs-replace is really a cost-per-mile comparison. The $2,800 repair buys you ~40,000 miles, so the repair itself is 7¢/mi — before counting the value your old car keeps losing. A replacement car costs more upfront but spreads that cost over more miles — and it will still be worth something when you're done. Let's see which is actually cheaper for your situation.

The costs that move

• Capital cost (fix) = repair bill + what you could sell the broken car for today − what the repaired car is worth after the miles
• Capital cost (replace) = purchase price − resale value after the same miles
• Financing = interest you'd actually pay on a car loan during those miles (amortized, so front-loaded)
• Fuel cost = miles × gas price ÷ MPG
• Insurance differential = newer cars cost more to insure (almost always)

The classic mistake

"The car's only worth $1,500 — I'd be putting $2,800 into a $1,500 car!" This frame ignores that fixing it gives you a $5,500 car, not a $1,500 car (one that'll be worth less again after another 40,000 miles). The relevant comparison is cost-per-mile of the next 40,000 miles, not the ratio of repair cost to current trade-in value.

If a replacement car means taking on debt, run the debt vs invest calculator to see whether financing makes sense at your rate — or whether that money is better deployed elsewhere.