It depends. There are a lot of factors that could influence price.
Time. How long does this last? Does $30 mil get them a years worth of access? 5 years? 10 years?
Exclusivity. Is Netflix going to be the only ones who have access to these movies via streaming? Do others get rights, too, but Netflix gets to show first? How long before someone else can show the movies?
Same price for each movie or average? Are some new release movies costing them $50mil while others only $3 mil?
People keep bringing up the loss of Starz but I suspect that once that contract expired Starz started asking for a much larger (undisclosed) amount. The amount they paid Starz for movies was undoubtedly going to go up now that they have many more subscribers.