Supercharger would be the most, but it makes more sense to just get a Hellcat. But for normal people like me, a cold air intake, catback exhaust, 180 thermostat, and a tune seem to be some bang for the buck. Long tube header can help a bit too.
Supercharger with headers will run you just under $10k. Just saw a 2015 hellcat manual with 900 miles going for $47k a couple of months ago at the local dealer. I have ~$41K total in my 2015 RT (includes what I paid for it out the door) and I am not quite 500hp at the rear wheels. Had I had the funds today, I probably would be looking for a HC.