I don't get it either. what is the world coming to? you own a car, but you're not going to spend a bit of money on it? what did you think car ownership entailed? freedom? it comes at a price.
A full tank costs you 50 quid, you might get 400 miles out of that if you're lucky. Tyres, for which you're going to want half-decent ones rather than the ditchfinder specials (perfect for those wet-roundabout accidental skidding sessions which kill hundreds of young people a year) are going to be 40 per corner for any half-way decent rubber, MINIMUM, if they're to offer any grip under all conditions, and you're far safer spending 60-100 quid. Welding? you're talking at least half an hours work, probably an hour or maybe 2, @ the princely sum of 50 quid an hour. You'll be lucky to get windscreen wipers for less than a tenner if you want two fronts and a rear.
And how much are you paying on insurance? new driver on a punto, male? 2 grand? 5 grand? and you can't spend a couple of hundred on making the car roadworthy? no wonder my premiums are so F888ing high. are you even insured? taxed? you know half of petrol forecourts have ANPR nowadays?
Scrimping on this stuff can cost you your life, can get you a criminal record, and destroy your career before you've even started.
Welcome to the real world. Enjoy your stay as an adult. Have fun, but be safe. Cars are really flippin expensive - get used to it sooner rather than later.