I bought a set of 2017 rear calipers from Ebay for $100. They came with the parking brake cable, used pads (like new), mounting brackets, and OEM brake lines. I have been on different Toyota sites comparing the rear drum to disc brake parts, it seems all I need to get next are the rear splash guards and brake discs.
My main reason for pursing this upgrade is for the bling factor. Drum brakes look so ugly when you do away with the hubcaps and put after markets wheels on. I will either be powder coating or painting the calipers and adding the TRD stickers all around BTW.