Other than paprika, the most economical way to add a color and signify a hot or spicy sausage would be to use red collagen casings. These casings look awesome when making hot links, or other spicy sausage. It doesn’t color the meat itself but the casings in red make the sausage look great!
You might be able to use a food safe food coloring. I don’t know if it would have any effect on the texture of the meat, and we’ve never tried it here, but it could be worth doing a small test batch on to try and test it out.
Other than those options, there is nothing else that is cost effective for making small batches of homemade sausage. My personal recommendation would be to use the red collagen casings.