Adobe has a good introductory discussion on Flash Media Server and some of the things to look for regarding delivering Flash video content.
http://www.adobe.com/devnet/flashmediaserver/articles/fms_hosting.html
Another great tool to determining bandwidth, bitrate, is the Flash Video Bitrate calculator at http://www.adobe.com/devnet/flash/apps/flv_bitrate_calculator.html
Here's an example:
I want to present video on my website. The size will be 547px x 307px (16:9). If I had 50 users a day see an 120 min video, how much bandwidth would I need? How much storage?
Once you determine this, you can estimate your hosting/bandwidth costs for using a solution like AmazonS3 & CloudFront to deliver. (http://aws.amazon.com/)