I drive a 8 GSR for a daily. No mods apart from a 8MR metal bov(because the old one was damaged), washable panel filter and 9 bodykit.
Not a drive goes by that I regret.
I still get 450kms average to a tank with squirts here and there and 500kms when i was really babying the car. Interstate driving got me close to 600kms to a tank. I went with a 8 for the extra gear. Now this is with australian weather conditions so it might differ to our hot and humid environment.
My putra when still standard with 4g93 sohc(lancer coupe here) returns about 500kms to a tank for city driving. So its not that much less compared to a NA car.
I'd focus on ensuring the drivetrain is A-OK! If the AYC pump/transfer case/gearbox fails, things are going to be expensive. It is not hard to have these fail either, ignore specified fluid change intervals for these components and you will end up with a bill just as expensive as an engine failure. Mind you, the 4G63 engine is more common than the AYC/transfer case/gearbox specific to an Evo. Also these components require more frequent fluid changes compared to a normal AWD car.
The other thing to check is undercarriage rust. If you see signs of fresh black paint underneath, stay away.
Other than that, good luck hunting and enjoy the drive when you get one.