You want to use Fraps or a similar tool to record gameplay? It has been designed so that a mechanical HDD will work fine with it. For $100 you will be getting a 40-60GB SSD which will fill up fast when recording gameplay. I would just get the biggest 7200RPM drive you can get for $100, and you should be set.
Right now I dont know how fast my mechanical disk is. It scored a 5 in the windows test so I am sure its slow. When I play skyrim I run at 60+ fps, but when I record it knocks down to about 10 fps so I know my hdd right now sucks, I didnt think about it when I chose a cheap one when I picked out my system.