Well you are where you are:
I assume you have used this site to find quotes. Have you made all the adjustments to the cover that you can which might reduce the premium. Increased excess is the obvious; 3rd party only maybe; adding your Mum as a named driver.
After you have done everything you can to get the premium down then you can do no more and will just have to bite the bullet. It may be better to postpone the new car for a year untill you become a good risk again in the insurer's eyes. That or buy something in a low insurance bracket.