There's no such thing as a cheap high speed / high resolution camera.
Here's a resource for rental or purchase:
http://www.visionresearch.com/
"Also I've heard about some software called 'twixter' for After Effects, which fills in frames in slow motion" - A.G.
Twixtor makes some fine plug-ins, but capturing the image is going to give much better results as opposed to interpreting the data between two points in time.