Well, I designed it and took the graphic to http://www.vehiclestickers.com
and the guy that runs that place cut the vinyl. However, you may want to look for a better option.
I originally contacted him explaining EXACTLY what I wanted and pointed him to the knotwork I had posted on my website He replied that it would be no problem. So last Satuday about 10:10am (10 minutes after they opened), I took the graphic down to him and asked him what he thought. He was impressed with the graphic and said it should take no more than a 2 and a half hours. We went to Barnes and Noble, looked around, went to lunch, sat and talked for awhile, went back to the place, and he had a test one done. It looked like a grid. As you know with knotwork, the strands are supposed to look like they go over and under, etc. When I asked him about the weave, he said it MIGHT end up looking right once you got it applied.
In addition, when he was explaining how vector graphics worked, he was completely off. (I took graphics courses in college...I know what a vector graphic is and what a bitmap graphic is, and he was way off.) At any rate, I re-explained exactly what I wanted, and he said he would need to work on the graphic to make some of my lines darker. He said it should be ready by Sunday. Well, it was ready after church, but my wife and I had to work on it for about 45 minutes to make sure it looked right, and there were a lot of mistakes. Most of it could be fixed with a box-cutter and some needles, but it was a pain. My wife and I concluded that next time, we'd either take it someplace else or cut it ourselves, since we know what we want.
I would look online for a place that will let you bring your own graphic in, and has been around for a couple years. This guy is new to the area, and I wasn't too impressed with his professionality. Of course, now that he has done that knotwork for me, he's a little more experienced in the way of knotwork.
As far as cost goes, he charged me $0.15/sq. in. for the vinyl itself, and he'll charge you for all graphics work he has to do, either design time or cleanup time. Hope this helps.