It seems you could go to any local sign shop and get them cut to spec out of a vinyl? Since it is an add-on item it is most likely something of that nature from house of grafx. It is a real simple need here, I would think you could hand cut those from scraps at a local source for cheap, definitely worth a phone call or two with your local shops.
The cleanest and best option would be to have it painted, not my bag but if I would wanted it on my GC I wouldn't get some paste on adhesive product. It is a $42 cost, not sure what you are looking for, something that is cheaper? I am not sure how much you are looking at saving here the bar is set pretty low as it is, pretty minimal investment.
2000 TJ Sahara
2015 Grand Cherokee Summit (6 cylinder Gas)