Parts aren't bad for Toyotas as long as they're one of the popular models (like a Camry) and built in the US. Parts were kind of expensive for our Cressida that was actually built in Japan. It was also a fairly rare car in the US, like I expect that the SC300 is.
My Camry's cruise control is occasionally failing when it's hot and you're out on the interstate going fast. Mom's mechanic said drive up to Nashville, pull a unit from a junked Camry, and it shouldn't cost more than $200. Plug and play installation, too. But Camry's are much more common than the SC
series (which is RWD, isn't it? It's not a Camry platform, I believe).