Well first thing is definately needs a new pattern part radiator, get the bumper off and double check no further damage behind, ie air con rad or cooling fans/motors, once that's fixed its driveable again...but make sure no sharp edges likely to injure a pedestrian.

Then its a case of asking at a little one man his dog bodyshop...without carpets receptionists and umpteen managers, and hopefully by recommendation...what he thinks about the bumper, might be repairable or it might need a new pattern part or even a used one which will no doubt need painting but he's the man to ask, will need a new grill trim.

You're right not to involve insurance, even with £300 excess i doubt i'd claim for under £1000 worth of damage.