I'm looking to buy a rotary tool to sand and detail small parts (dense
foam and plastic). I've seen some cheaper rotary tools and am
considering them.

http://cgi.ebay.com/ws/eBayISAPI.dll...ayphotohosting

Here's one I've seen at Target. It has a lot of the grinding bits I
would use and a flex shaft and its only $25. Would I be throwing away
my money if I bought something like this? Should I go for the Dremel
instead? (similar Dremel set would cost $75).

Thanks