I don't have DISH but LP comes out to about $200 after taxes. It's actually like $20 less if you get Early Bird. I don't know about DISH but my cable provider also let's you split it into 4 monthly payments, which makes the overall payment more b/c you are paying separate taxing fees but it's not much more that you'd notice.
No, they do not show every game. They show every game that doesn't come on national tv (channels like ESPN, TNT, NBATV). They also have "blackouts" and those are games that are televised on a local channel... in my area, if Celtics play Mia or Orlando I have to watch the games on the channels dedicated to showing those teams games (like FSN). Those channels are usually labeled "basic" which means you get them no matter what. With my provider I have to pay for separately for NBATV.
Given how bad Celtics were and were projected to be when making national tv schedules last season, I'd say we had less than 20 nationally televised games. The NBA puts the best teams on nat. tv the most, so don't count on us being on there more this season given the names on our roster (they make tv schedule prior to seeing how good the teams actually are). Before last season, you could probably get away with not buying LP if you weren't in a local area b/c we were on nat. tv a lot but if you want to watch a lot of the games, I think it's worth purchasing (unless you are one who didn't enjoy them last season).
You could just watch streams online for free but that's illegal and not any of my business lol.