I'm in the process of buying an Evo IX with 116k miles and I just did a compression and leak down test.

Cylinder 1: 150 psi - 9%
Cylinder 2: 140psi - 11%
Cylinder 3: 125psi - 25%
Cylinder 4: 145psi - 9%

Unfortunately it looks like cylinder 3 has low psi and a bad leak down. We heard the air come out of the exhaust tail pipe. Anyone know what this can be and how much it cost to fix?

Ultimately, is this car worth buying? Everything else about the car is in pretty great condition.

 

Given that you heard air escaping into the exhaust, that would point to a leaking valve. This could also be part of the low compression in that cylinder as well.
I'd guess that it needs a valve job so that means pulling the head for sure.

The price is highly dependent on how much of the work you do yourself. Pulling the head, taking it in to get valves done is a lot different than having a shop do the whole thing. You could call/email a trusted shop local to you and get an idea of cost.

As for if its worth buying that's basically down to you and the price of the car. At the end of the day, a leaking valve isn't too bad of an issue assuming the rest of the car is in good shape and the deal is decent.

 

Sooner or later everyone will need a rebuild, the whole power/drivetrain, I factor that in when buying a used evo

 

You can do an OEM shortblock and rebuild the head for about 10-12k installed.