[turbo6bar]

Plug-n-play and under $475? That's a tough one. You can certainly save money buying separate bits, but you'll be trading time for dollars. I'm thinking <$200 for separate temperature PID and relays, but it's not plug-n-play.

You could replace your contactors with eBay ID: 250355943670, but there are so many others that'll work just as well. Add some heatsinks to those relays.

Then, you'd need a temp controller, $30-150 (used-new), and you'd be ready to go with some wiring and testing.