There are some threads about what you have to consider when designing a tartan. Someone will share some links.

I have no experience yet, I'm considering but the costs are holding me back.

Some kiltmakers that offer the special weave:

Obviously our own Matthew Newsome and Scotweb. Don't know about the other North America based advertisers.
Hector-Russel and Nicolson Kiltmaker do, but I think only with registered tartan. Maybe if you ask you can safe some $ with not registering.

Hope that helps.