Fortunately, this achievement isn't nearly as bad as it might sound. You only have to finish first ONCE in each of the 61 unique events. There are a total of 51 events from the beginning of the game, and the Most Wanted races are the remaining 10 events.
Each car has access to 5 different events. Each new event will require you to drive to it's location to start it. You can jump directly to any event you've played previously. You can see a complete list of events you've found on the "Recommends" map. Any events you haven't won yet are indicated by a bright green square.
Here's a condensed chart of all the available events and which cars have access to them by ratchet
: 12/18/12 UPDATE:
The multiplayer update patched the glitch below. Any cars you've already done it on will still have the mods applied to them. You can just delete the update and still do the glitch.
Sometimes you'll have to replay some events, just to unlock mods to make medium/hard difficulty events doable. There's a way to avoid this by using the Mod Transfer Glitch
. What this does is, it allows you to copy your mods from one car to another in singleplayer. Using this exploit, you can unlock all the Pro mods on a car ONCE, then copy them to ANY other car without having to unlock them again!
1. Switch to a car you already have mods unlocked on, and equip all the mods you want to copy.
2. Open the map and cycle to the RECOMMENDS map. Pick an event and select the car you want to copy the mods to.
3. You now have all your pro mods on the car you chose, without having to unlock them on that car.
That's all there is to it. Now you can complete all 5 of that cars events with ease.
Keep in mind, these aren't permanent unlocks. If you switch mods on the car you copied to, you won't be able to re-equip it until you do the glitch again, or unlock it for real.