$70 for 400-450 kms fuel, rego, insurance, services etc etc
plus the inevitability that you will modify it
i reckon if you can put $200 away a week go for it (unless you dont want insurance then less)
but be prepared to spend $500 on tyres when you fry them or $600 for a new clucth when you rape it
ahhh but who cares bout the money just buy one and mortgage your (or your parents) house for it lol