I'm a keen cook, and I've wanted to experiment with sous-vide forever. But "proper" sous-vide machines cost a fortune. So I was quite excited when my son pointed me to a Kickstarter for a cheap sous-vide, Codlo. The basic idea here is to use a slow cooker or a rice cooker for the water bath and an external thermostat to switch on/off the mains supply.
I was about to fund this thing when I realised I already had everything I needed to make my own at a fraction of the cost. How? I'd already bought an STC-1000 thermostat (US version) for a wine cellar I'm building (that's another story). And I already own a slow cooker (which I don't use, because I don't really go in for slow cooking) - a Russell Hobbs 14586 (no longer available, but there are many alternatives, for example, Morphy Richards 48710).
The thermostat is overkill, because it does both heating and cooling, and for this purpose you only need heating. But it is cheap. So, given those two ingredients, all you need is to wire it up. Probably the simplest way to do this is to use two extension leads (or one computer power cable and one extension lead) - here's a long but thorough video showing how to do it. Of course, for sous-vide you only need to wire up the heating circuit. Also, if you don't mind having to plug it in twice, you can avoid most of the soldering and heat-shrinking - or all of it, if you use Terminal Block.
The other ingredient of sous-vide is vacuum packing. Sadly, I missed another perfect Kickstarter , but I've found you can get away with just sealing freezer bags almost completely closed, then almost completely immersing them in a bowl of water (obviously without letting the water in!) to drive out most of the air, and sealing them before you take them out of the bowl.
So there you have it, sous-vide for a total cost of about £40 ($60) and about half an hour of fiddling. All that's left is to start cooking things! The web has plenty of sources for times, temperatures and recipes.
By the way, please be careful: mains electricity and water don't mix! Finally, do note the safety advice.