I get a lot of my OEM parts from Toyota Parts of Dallas (Texas)
ToyotaPartSales.com
Throttle cable is an expensive item and what I think my source quoted me it's about $150 plus shipping. They are still available. The fourm's parts vendor may or may not be able to improve upon the quotes already noted. If you can find a good used one then that may be your best bet... but that's the risk - finding a good one.
I agree with the BGB and bleeding of the cooling system. I'd start here as you don't want to have to go much deeper than that if you don't have to...