What is the best cheapest non latex form of contraception?

Basically me and my girlfriend have had a few times with normal condoms and the last time she got a really bad rash, what do i do? wer both clean.. wer virgins... so is it definately a latex reaction? and neither of us have a huge amount of money since wer at uni since the non latex ones are 7 quid for 5 thats unfair is ther anything we can do/try?