(I'm reposting as my previous thread was deleted due to linking to ebay.. Hopefully google image search link is okay.)
Did you know that hair-straighteners have 2 PTC temperature controlled plate heaters that maintain 220C-230C (430F-450F) surface temperature?
Like these: https://www.google.com/search?safe=o...nt+temperature
Thats a mold preheater right there, isn't it?
They are made in different sizes, wattage, set temperatures, many work direct from mains and need no PID controller.
They run around $5 for a pair on ebay.
They are so cheap that could be permanently attached to the base of the mold.