I also just built a yeast stir plate and replumbed my mash tun cooler. I only bought one part for the stir plate - a potentiometer to slow the fan down. The parts used were a wooden cigar box from a friend, an old PC provided a fan, hard drive magnets, and an old cell phone..the power cord with transformer. Throw in some gorilla glue, a few wire nuts and odd screws and slap it all together. Here it is with the fan mounted to the lid before I added the potentiometer to slow it down.
For the mash run I had been using plastic hose clamped onto the existing cooler spigot but it wasn't sturdy enough. Tore that spigot out and replaced it with a nipple, two washers and two bushings and reattached the valve to the outside bushing.
Next I want to pick up an aquarium aerator and a submersible pump to use in an ice bath to feed my wort chiller. The hose water here is too warm to chill the wort quickly or low enough.