Hi Tom, you may have been better posting this in the Film category.
Here is a link I found that will show you how to make your own, for the price of a macro lens (if you don't already have one)
http://www.scantips.com/es-1.html
The thing is, you can buy a negative scanner, but they are usually low resolution (5mpxl), however, if you already have a 10mpxl camera.....
The only thing i would add is to get/construct a light box that goes behind the negative. This way, you have a constant temperature light source. The advantage being that all your RAW processing can be done in batch mode as you should be able to select the same White Balance setting.
It will also be faster than a scanner (slide, click, slide, click), and you don't need to keep checking your PC after every slide.
Just my 2p.