Question One: RSN (Regional Sports Nets) would be just that, networks devoted to pro and college teams in a given market. IE: MASN is available (primarily) in the mid atlantic area; DC, most of Maryland, parts of PA and VA. It shows Oriels games and what-not. As far as the sports alt channels, those are used for when some regionals have two feeds; but I believe they are mainly used for things like Center Ice and other sports packs. Generally the RSN's would be: MASN, MSG, The mountain, Comcast Sports Net (xxx), Fox Sports (xxx), Big Ten Network (according to Dish), and a few others I am forgetting.
Question Two: The RSN's are subscription based channels not OTA channels. The primary way to get an RSN with dish is to be subscribed to Classic Bronze Plus or higher (AT100+ or higher). Then, which RSN's you get are based on your zip code and county.
The only way you'd save money is if you are on the classic bronze plus or AT100 plus programming pack (or you are subscribed to the multi-sports pack).