You mean, $8-10 per month, not per disc you rent, for rentals from Netflix and BlockBuster, and with the way the queues work, if you find it sucks at the first disc, you can just remove the rest of the series from the queue right then, and move something else up in the queue to watch. Also with the watch it now for some of the stuff, you don't even need to wait for the discs to arrive in the mail.
If you were to spend the money you're wasting on bad DVD purchases on subscriptions to Netflix and BlockBuster, you'd end up saving money becuase you'd end up buying fewer bad shows.