I wear a mixture of smart trousers and tops with a cardigan, jersey (including boden) dresses and boots and suits. I get ALL my workwear from ebay - set up searches for the labels and sizes that fit/suit you...
Even with my suits though, I never wear any 'button up' type top, they just don't suit me, so I got for smart t-shirt type tops or short sleeved jumpers instead.
I would start looking for a suit of some kind now - even if you DON'T need it for school you're going to start needing it for interviews during your course (which could be sooner rather than later if you're maths, or science, or all the other subjects which seemed to get jobs before mine did!).
For goodness' sake go with COMFORT over everything else with shoes - you really do need to be comfortable - depending on your school set up you could be running all over the site (ours is HUGE), plus you can't under estimate how much ground you cover when you're walking around and around your classroom checking pupil's work and interacting - go for comfort! You can get really comfortable smart shoes from somewhere like clarks, and that's where I'd prioritise my budget, to be honest. As mentioned further up the thread, you can pick up loads of bits from supermarkets like asda or tesco for very little, but get your feet right!!
Have a few thermals handy too (I can't be the only teacher in a 'mobile' classroom (read small hut))?
Good luck! It'll be very full-on, but there's nothing like it! I'm about to go into my second year of teaching (so did NQT year last year) and I'm just about to turn 39 :)