That is really shitty man, I have zero personal experience with this. But, I think, the airline
should
be responsible for the entire amount to replace everything. It is their job to get your bags onto the right planes and too your destination, and I'd imagine it's a pretty penny to bring a golf bag with you on a flight now a days. That is their responsibility and they should be trying to make it right for you. I know you'll get a lot of grief and it sounds like in the end you'll only get a fraction of what it'll take to replace all your stuff, to me that's bullshit. I do feel sorry for you though, I would be so pissed if my whole bag was just gone.
When I was racing motorcycles across country one of my team mates bags was lost, he got his back a couple days later after the races where over but he just had to use borrowed gear. There was probably over 2k in the bag worth of riding gear, helmets, boots, ect. So there is hope of getting your stuff back, I hope it works out for you.