There are a total of 80 collectibles. When you reach Level 20 in Respect you can buy the Collectible Finder for $49,500 from the Upgrade section of your phone. The Collectible Finder will allow you to see every collectible, but only through your mini-map. However, if a collectible appears on your mini-map and you don't pick it up, you'll be able to see it on your main map. It is best to purchase this upgrade early so you will have all collectibles on your map by the time you are finished doing the Activities and Challenges.