No need to pay any money to convert something to flash video (.flv). Plenty of great free open source options out there.

Pazera does this just fine, for free. I've used it on a bunch of videos, has converted mpg, avi, pretty much everything I can throw at it. It's basically a nice front-end to ffmpeg, mentioned earlier, which is an open source media converter.

Free Video to Flash Converter 1.0 - Convert video files to Flash Video (FLV, SWF), AVI to FLV, AVI to YouTube FLV converter - Jacek Pazera

You can play with the settings in pazera like frames per second and encoding bitrate, even video size, to help you balance size vs. quality. I get huge files too coming off of Sony Vegas, but Pazera can reduce it down with no problems. And it runs on Windows.

Jeremy Zerr
Transform Your Internet Business - with Free Software