Have you looked into whether you can get a reduction in the court fees? If you are on low income or claiming certain benefits then you may be entitiled to £175 off the fee.
Make an appointment at the CAB to see if you are elligible for any help with the full fee.
If you're not on low income or benefits, then it's just a case of saving a little each month I'm afraid as you need to pay the fee in full to be declared bankrupt.