Rather than pay upwards of £75 it's easy to make one of these at home.
You will need:
1. An old computer hard drive. The older the better - I used an ancient 420mb model. Take this apart and you'll find several powerful neodymium magnets. Careful with these as they can pinch a bit. Also, keep them away from credit cards etc.
2. An old computer fan with a speed control.
3. A tupperware box or similar.
4. A power supply. I used an old phone charger.
Attach the magnets to the fan and mount inside the box, then attach power supply. That's it! google 'homemade magnetic stirrer' for more detailed instructions.
You'll also need a suitably sized stir bar. It's possible to make one of these, but it's easier to buy one from e-bay. You need an egg shaped one if you're mixing in a round bottom flask, or a bar for a beaker or Erlenmeyer.
Hope this saves someone some money. It's also cool to make your own stuff!
Sounds interesting... I guess I went the route of buying a used one on ebay, which also works... I paid 25 Dollars...