OK, so what type of surgery has been reccomended?
If he's under a year, a TPO (Triple Pelvic Osteotomy), if he's eligible, from what I've researched is the least invasive and has the best results. IF DONE EARLY ENOUGH! This is when the femoral head is not fitting completely into the acetebulum. They break the hip in three places, inserting the femoral head into the acetebulum, than placing metal bars and screws to hold it in place. The bone heals, but he plates/screws stay put throughout the dogs life. This is the preferred surgery for severly dysplastic dogs that have been diagnosed early. There are some requirements, age of course, preferrably under a year, and with little to NO wear and tear on the joints. This being because, there is no actual change to the head or acetebulum. If there's too much wear on the joints they would do a THR (Total Hip Replacement)
Cost (I'm in CA, so they may differ a few hundred

) - $4000.00
Total Hip Replacement is around $3000.00/hip.
Nowadays, if it's a specialists, the risk during SURGERY are pretty low.
The real issues arise during post-operative care. With both surgeries, usually the dogs have to be on crate rest for around 6 months. This means, IN THE CRATE, except for quick pees/poops for the WHOLE 6 months.
It may seem like a long time, but from the people I've spoken to, the difference it made in their dogs lives.. they've said they'd do it again in a heartbeat. Even looking at pictures of their dogs stuck in crates for weeks on end, and they'd still tell you, I'd do it again.
What is his type of HD?
Shallow acetebulum? Mishapen Femoral Head? WOrn down femoral head?
How large is this dog?
The other option is FHO (FEmoral Head Osteotomy) which lately has been done on larger dogs, but most specialists will not reccomend it. This is when they cut the femoral head completely off, and the ligaments and muscles are what keep the hip working. Not exactly in the best interests of a larger dog.
I'm sorry to hear about your pup.