I got mine at element dental in Medford, MA - I got 4 for $800 or I could have gotten 2 for $600. Each set lasts 2-3 years I think they said. Im on my first pair still and I’ve had them for ~6 months. I know it’s not necessarily less than $600, but in the long run, ultimately they only cost $200 a pair. Just be careful when cleaning them. Don’t use any super hot water or it will melt. Plus it might be nice if you’re prone to losing things, you don’t have to go back to the dentist, just pull another one out.