Get an electrian, you can do the work yourself as stated, then pay to have it checked, which will get you a cert. Your insurance is no more than a piece of paper if you or a mate just does it.
If you are a member of AFO (see above) you may be able to borrow / hire from another festival, both genny & leads, the kit may well be pat tested & carry certs. Otherwise try the hire shops, not cheap but safe & certificated, perhaps a reduction for sponsorship?
There is no safe way around this one.
Think about prison food & the showers!
Skipy.