so you're not just asking about pixel size but also disk size? 10 MB... you'll want to save to H.264 or similar (mpeg4, divx). Not at initial rendering, but with conversions later. You can easily fine tune the rendered clip's conversion with ffmpeg, trying various quality parameters like

-qscale 2
-qscale 3
-qscale 4

etc... to see at what point you get below 10 MB and still have good quality.
http://www.thebest3d.com/ffmpeg  has info on ffmpeg and WinFF, a free front end which uses ffmpeg (includes it, actually), in case you don't like the CLI (command line interface)