If you leave this right till the end of the game you can just click through them all in one run as you'll have more points than you actually need.
On the main menu under the garage option is where you'll the unlockable bonus content. Choose the option on the right for film.
The are four sub-headings; Behind the Scenes, Unlocked Cinemas, Photo and The Cast.
Behind the scenes has 28 items to unlock at 350 points a piece which totals to 9800.
Unlocked Cinemas has 8 items to unlock at 200 points a piece which totals to 1600.
Photos has 140 items to unlock at 200 points a piece which totals to 28000.
The Cast has 9 items to unlock at 150 points a piece which totals to 1350.
When you have purchased all of these items at a total price of 40750 you need to go back to the main menu for the achievement to unlock.
If you have also purchased all of the 'Game' unlockables you will also unlock the achievement for Behind the Scenes Bonus DVD