my university wants all of us to learn a new instrument so i want to choose to learn to play percussion!!
what instrument do i need to buy actually(do i need to buy a marimba??????) and how much is it going to cost me? i want to play it to professional level!!

I'm learning Marimba for a grade one-a-thon (except I'm doing grade 2) Loving it!! Its got such a wonderful sound.

the guy who is teaching me got a four octave marimba from america through ebay for about £200 or something, not bad considering the usual price!!

I would say that most percussionists don't own a load of percussion instruments, so buying a marimba won't be necessary if you have access to one. Does your uni have one that you could practise on? Buying one is quite impractical as they generally cost more than about £4000 (and can go up to £10 000)!