So every student will dress up in fancy dress gear at least once a term - don't go spending too much money though on a costume you're likely to wreck. Some of the best places to start your search are charity shops and places like Poundland where you can bag yourself a bargain. Below are some tips on saving some cash on your costumes:

Pirate:

So the trick here for guys is baggy trousers and for girls you need some tight 3/4 length jeans. Then find yourself a frilly blouse (guys try the women's section in places like Primark) with no collar and and a few buttons down the front. Then try and find an old waistcoat in a charity shop and when you get back home burn the edges and 'ruff it up' a bit with a pair a scissors.
For accessories like a bandanna try Primark, for swords and pirate hats try somewhere like Poundland where you can pick stuff up for next to nothing.

School Disco Night:

School uniform is one of the easiest - all you've got to do is pop down to Primark and get yourself a white shirt for £4, pair this up with your old school tie and a pair of jeans/short skirt and your outfit is complete! Girls can add a little extra by tying you're hair in bunches.

70's Night:

This is pretty simple for girls - just get yourself a pair of flairs and pop down to your local charity shop for a bright, multi-color baggy blouse. If possible try and cut a strip off the blouse to use as a headband.
For guys you need to try and get a cheap, bright blazer/suit jacket from your local charity shop. Team this up with a shirt with the biggest collar you can find, together with some jeans (or flairs if you want to go to that extra expense). If you're going wild why not buy yourself an afro wig from a joke shop and some round, rose-tinted shades.

Roman Toga Party:

This is one of the cheapest student costumes and is pretty much the same for guys and girls. Just buy yourself a white sheet from somewhere like Tesco or Primark for a couple of pounds and tie it round you - just wear this with flip flops/sandals and you're there. Jokers Masquerade sell Roman Gold Laurel Headpieces and swords for £2.99 each which is a bit of a bargain if you want to add a little more to your outfit.

Cowboy/Cowgirls:

You're going to need to get yourself a checked shirt - a charity shop will be your best bet. Then pop down to somewhere like Poundland or a toyshop and get yourself some toy guns (a rifle and a couple of handguns) and a cowboy hat - this should only cost you about £5. If you're prepared to spend a little extra get yourself a pair of chaps as well from a joke shop, and try and find someone with some cowboy boots! You can also get yourself a bandanna to use as a neckscarf.

Superhero Customes:

I'm afraid you're going to have to buy a specific costume if your planning on being your favourite superhero for the night (unless you're pretty nifty with a sewing kit!)