Is there a cheap way to get this ring for cosplay or if too inauthentic in appearance where can I have it made for a reasonable price?

You could probably create one yourself quite inexpensively, but it may not look too good (depends on how much work you put into it). Unless you know of a jewelry craftsman in your area, I think you're stuck to your own abilities.

If you're going to ask a craftsman about making one, make sure you draw it out and give a solid explanation as to how you want it to look and what material you want it to be made of. Make sure to measure your ring size, as well.

There's a few cosplay oriented jewelry shops online that might have something close to the image but if you are concerned about cost you could make one very cheaply you just have to invest time making it

you can find shield shaped signet rings to start with a base to build on