To answer your other questions, yes, I would recommend getting a mixer to run your mic through...it'll give you more control over the sound you get, and you'll get a "cleaner" sound. Also, as you get into the upper-end of mics, you'll find quite a few that require "phantom power", which a mixer will provide. (This is usually the case with a good condenser mic.)
As far as how far up you want to go, mic-wise...I wouldn't go too high-end... a good condenser will pick up a cockroach sneezing three rooms over. If someone's running the television too loudly in the next room, it might give it false input.
And the Radio Shack model is their standard little workhorse mic...
this little fella. (Again, as I said in my first post...your mileage may vary.
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