Ohhhhh if only I had saved up money from my placement year, we're going to Val Thorens the week after with uni for £350 - I'd of happily driven to Tignes for that week and then met uni the next week, but I'm only just going to be able to afford the week in Val T
OP: When are you going? I don't remember my school/6th form costing much more than £500 - but we stayed in crap hotels mainly, although we didn't care as it's the skiing you go for. That included lessons and hire. That was the back end of the season too, only half the runs were usually open as the snow was melting - but it was good enough for our needs at the time.
We were also given catalogues for companies who rent out clothing, can't remember any names of them though - but it may be worthwhile asking your college about renting clothing rather than spending more money on buying your own kit as you may not enjoy it and never get the use of it again.
If you do buy your own kit, TK Maxx is the place to go. No need for thermals tbh, I've never needed them in the 7 or 8 times I've been. Just a long sleeve Tshirt (maybe a short sleeve Tshirt under/over the LS one if it gets a bit chilly) under my jacket, but I always have the vents on my jacket open.
The two areas to spend more on are socks and gloves imo, I've got some K2 socks from TK Maxx that were a few seasons out of date (not bothered about anything being out of date, but socks?? C'mon!) for pennies and they're fantastic. I've just got a new pair of gloves after shredding mine from trying to learn 360s last year and walking back up 100ft dragging my skis behind me, think I paid £50 or so for my last pair and the new pair. Never had cold hands, apart from when I dropped them in powder and it went inside my left glove
I'd go goggles over glasses too, as long as you have a decent pair (mine were £115 or something daft, and are fantastic) plus you may want a bandana type neck-warmer if you're sensitive to the cold air like I am (did half a day in Val T the other year as I forgot my bandana, couldn't hack it any longer!)