I am toying with the idea of making my double into a triple. What do I need to accomplish this?

I have 10 speed shimano STI with 12-27 ultegra cassette and 50/36 Truvativ crank.
Short cage ultegra derailler and a 10 speed Shimano 105 chain.

From what I can gather, I need the triple crank(duh), long cage RD, and a triple compatible left brifter. But it looks like it is going to cost at least $500 for the whole kit and kaboodle!