I went to Peru with World Challenge in 2009. Put simply, it was the best experience of my life. The fundraising was a challenge, but my group worked well together and we did a lot of joint fundraising.
WC help a lot with the fundraising, and unless it has gone up considerably, £6000 is an over estimate. Much of the kit you can borrow/get second hand/get very cheap at decathalon.
I managed to raise about 3/4 of my money by washing cars, feeding pets, doing a sponsored absail (organised by WC), getting sponsorship from companies, donations and I didn't get a job until afterwards. I topped up the remaining amount with my bank account and inheritance.
Don't forget that this is one of the best things you could have on your CV, and my personal statement for uni was almost entirely written about this (talk about the skills you gained etc) (I got 5/5 offers).
Thats just my two cents anyway :-)
PM me if you need any help/advice etc.