There are a lot of "ifs" in pricing based on the condition of your parts and what replacement parts you need.
For head work, I would expect to pay a minimum of $450 labor and that would be if you do not need guides/seats replaced. For that amount, I would expect a head back that was shimmed and ready to install. Short of valves, parts for the head are reasonable in cost. The shop doing the work can probably supply all the parts, except valves. If they don't usually do KZ1300s (don't know any that do), then you may have to point them in the direction you want on replacement valves. I *strongly* recommend replacing the valve springs. Springs wear out. Yours are 40 years old. I replace valve springs on our race cars every 100 miles or so and you can tell the difference - the KZ turns high RPMs....
For the cylinders, if you just need a hone and fresh rings, I would expect to pay $10-$20/cylinder. If you need to bore it, $20-$40 cylinder. If the latter, you will need new pistons as well. Add a few more bucks if you want the shop to gap the rings for you.
Parts can be expensive and there are lots of opinions on what parts to use.
I would ONLY let a bike specialist work on the head. Preferably a KZ shop. I have no experience with any of them, but would look for someone like
www.pitstopperformance.com
or redlinecycle.com. Having your local machine shop do the work is a recipe for disaster - this is probably way outside their normal work.
Take care in shipping the jugs. Folks have had the liners break during shipping. If you ship the head, ship it with the valve cover bolted on.
