Gizmo needs surgery

Hi this is our Gizmo. For the past 18 months he has had an ongoing problem where his bladder gets blocked and can not pee. He is on all kinds of medication to try and help but the death of our gorgeous, elderly, fur baby Cole at the weekend has caused him so much stress that he is again unable to urinate. The vets have decided they need to operate as the medication is no longer enough to keep him well. Due to the time span of this ongoing issue, our insurance have now declared we have reached the limit of cover for this condition. They will pay £421 pounds towards this surgery which leaves us a shortfall of £2800 + . He is only 6yrs old and we want to give him the best chance of a normal and pain-free life as possible. He is at the vets and they have catheterized him for the umpteenth time to make him more comfortable and he is awaiting surgery which they have scheduled for tomorrow. We love our fur babies unconditionally. Losing Cole at the weekend has broken our hearts, we can't lose Gizzy too. Please can you help?