Well I hate to give away secrets but here is my opinon. Take an old disc or a new disc from a new or used farming equipment shop. I think you can find almost any size from 8" -14" discs. You will need a oxy/acet torch, a welder, and a grinder. cut a piece of steel big enough to cover the center of the disc and weld it in place. Then take either some flat stock or some round stock and bend it in a "U" shape. weld it onto each side for handles and you have a cowboy wok and I would be willing to be that you could almost spend close to $50 total for set-up. I would imagine that discs are not but maybe $20-$40 a piece. For $300 you could almost buy a welder, grinder, and a torch.
The next best thing to a cowboy wok is just a piece of steel. Take a rectangular piece of 1/4"-3/8" plate steel to your next deer camp. You can make it any size you imagine( probably 3'X2' make sure you can lift it). Now get your camp fire rockin. Once you have established a good coal base, scoop some coals in one corner of your fire pit and lay the piece of steel over the corner. This is great for steaks, taters, a pot of beans or chili, a pot of coffee, eggs, and whatever else "camp cookie" brings along. Just make sure nobody uses it for a chair cause they might get a case of the red a#@.
To wrape this book up IMHO you can do a lot more creative things with $300 then buy someone else's cowboy wok. Have fun