my friend has a r34 GT and gets about 550kms-600kms on a full tank with mixed driving conditions. thats to empty. costs about $80 if tank is empty.
my r32 gtst costs about the same and will do 450kms. R33 gtst's are even better with fuel considering they have more power and bigger capacity. r34 gtt's are better still considering they have 206kw's. turbo's will always drink more then a NA obviously but if you want a turbo skyline fuel shouldn't be a worry.
I'm 20 and a student. work casually at my local kmart. i make sure every week that i will have money for fuel before everything else so that i can drive it. Owning a skyline has been a dream of mine and now is a passion.
If you are worried about fuel then go for a NA 34.
rexys are nice, sound good although i think overated, heavy and expensive to repair although i might be biased as i'm a evo boy LoL.