Did you try rinsing the rice really well before cooking it? I bought a cheap bag once that had that same plasticky smell and taste. I put it in a colander and ran cold water over it for a good minute or two, then let it sit in fresh water for another 10 minutes. Drained it again and cooked it, and the taste was gone. Might not fix every bag of cheap rice but it saved mine. Worth trying if you still got the rest of the bag.
Rinsing really does make a huge difference with cheaper rice! I always run mine under cold water for at least a minute until it runs clear, then let it soak for 15 minutes before cooking. That extra step definitely helps strip away any weird coating or dust that gives off that plasticky taste.