When my car was stock (fmic, filter, exhaust, etc), a full tank will take me to around 480-550km.
After a few mods here, upgraded turbo, full standalone ecu, etc, etc. A full tank was about 350-400km.
Actually its alright la, I guess it also depends how often you stay in the vacumm zone of the boost meter.
As for maintainence, what timing belt ? haha. SR20DETs run on timing chain.
And normal servicing is around RM 500-600 depending on what oils you use.
I only use 300V per 5000km, so thats why its a little more expensive but its worth it.
Actually if you use Motul's semi-syn + oil filter + labour, it'll be less than RM 200.
Clutch, drivetrain parts, well I guess its up to your driving style and whether
you really abuse the car or not. I'm sure if you drive like a granny, most of these parts
should not be changed regularly, but if you do drive the car the way it was built then
parts are not that expensive, a lot of second hand parts are available and they're reasonably priced too.
A new twin plate clutch is around RM 3800-4500. A used one would be RM 1500-2000 depending on condition.
The standard 6 speed gearbox is very weak, it's very prone to break at power levels more than stock.
Thats why if the car is 400hp, I don't think the std gearbox would last very long, or either the car is not 400hp.
Also you wont see many S15s with more than 350hp using stock gearbox, if they are, you know something is not right.
Actually for the S15, there's not a lot of maintainence involved la so it's not that expensive,
Its just that there are so many aftermarket parts to buy for the car, thats when it gets addictive to buy buy buy.
Any further questions, feel free to ask.
Cheers.