I bought mine from Northern Brewer a few years ago because for some reason big coolers were CRAZY expensive at the time and the Fermenters Favorites 10 gallon unit was on sale. I've been happy... reasonably sturdy, and drops maybe one degree during a 60 minute mash. It's really nice, which is weird to say because every single other thing by Fermenters Favorites that I bought has been hot garbage.
It's literally just a big Coleman style cooler with a ball valve where the pushbutton spigot would normally go, though, so if you can get a food safe ball valve and fittings, by all means DIY it.