Serious recommendations here without breaking the clothing bank.
Footwear - driving boots start at very low prices, a pair of karting boots are easily under forty quid, can be worn on the way there & back, are better to drive in than trainers as they have more feel (trainers tend to be air filled these days, I find them awful to drive in) and look the part without being excessive.
Gloves - for some reason I can't go on track without gloves but that's a personal thing. Don't go for the thirty quid cheapies they are pretty nasty (I know, I sell them!) but the <fifty quid entry level FIA Sparco and Sabelt which are much much better value. They are a better fit and just *nicer*! Be honest, if you can't afford the extra twenty notes you shouldn't be track day-ing!
Helmet - I'd always wear a balaclava, especially in a closed car. Nothing to do with protection as much as keeping your expensive helmet clean. When Nomex lining gets soggy from sweat it is HORRIBLE and takes ages to dry out, plus will smell for ever and a day. And if you're wearing a balaclava, why not wear an F/R one, they start at under twenty quid.
Chunder, that's getting you decently kitted out for track days without spending a fortune. If you want an overall, a polycotton one will set you back under fifty quid and is quite sensible when doing anything that involves older cars...you'll be working on them a lot, even if it is only changing wheels! Proban is of course flame retardant, and they're anywhere between eighty and 150, that won't break the bank.
There is a link to another company that sells this stuff on my profile
HTH
Max