I have used my Dremel for years, but last summer I found myself needing one, and mine is across the contry in storage. I purchased the cheapest one from Wal-mart for $8.88 (in a little metal case with bits) and have been using it ever since. While not as nice, or as good as my Dremel, it really was well worth the cost. I think if you plan to use it often and want the most options then just get a nice dremel (they really are not that expensive) but for the cost my cheap one has really proformed. That being said, when I get my Dremel back I will not be using the cheap one anymore (just saving it as a back-up). You could alwasy try one of the cheaper ones, and if you liked it, and wanted more, then you could invest in a top of-the-line model Dremel.
Just my 2 cents!
As for the bits I have never used the polishing ones. nor do I like the cutting blades - what I use most is the various sanding options (about 90% of the use is that) and the drill bits. All the others are really a waste for me so far.