chippy help me what to buy cause i'm going to b&h today .
i know i'm getting the audio technica lavs channel one suggested, but apparently i need a mixer to go with that?
The problem you might run into is with two lavs you are right at about $300 leaving only a couple hundred in your projected budget.
As such you might consider a basic field mixer such as the Rolls MX34, while not the top-of-the-line mixers they are reasonably quiet and being stereo allow you to pan each input to it's own channel on the 7D, the real down side is they lack any form of VU indicator requiring you to experiment with the levels to have it low enough to prevent clipping. That said once you get the levels correct you can place a couple of witness marks on the panel with a permanent marker and you will be good to go.