Sorry to hear about your dog ... My wife and I don't have kids yet, so Derby's pretty much our pseudo-child, so I know how much a part of the family they become.
Interestingly it's been about 50/50 when I tell people how much hip replacement costs as to whether they would do it themselves or not. It just wasn't an option for us to consider the alternative if we didn't get him the surgery.
The thing that I think is really great is the fact that total hip replacement would, from all I can tell, make him 100% (assuming there aren't complications). Considering how he's obviously not comfortable now, he would be "better than new". Another interesting thing is that apparently they developed human hip replacement techniques on dogs, so they've actually been doing it longer for dogs than for humans.
ms