Hi George
As with most stuff there are a lot of cheap copies out there stay away from them as you will get little or no support if it doesn't work. Just took a quick look at Ebay there is a Laptop with the software already loaded and the correct ODB cables for £185 looks OK to me. If your pretty good with software you can buy the software and leads for less but it sometimes can be fiddly setting it up.
Google should be able to help you with test parameters for the sensor, check the inlet side for air/vacuum leaks. A split hose or Vac line can often fool people into swapping sensors.
Dave