Information gathered from
There are a few ways you can do this:
- Once you get about 25k on any character you can find, steal and fully modify a cheap car such as Weemy Issi Compact (Mini Cooper) or Motorcycle (Western Daemon)
- You can wait until you unlock Trevor as a playable character and with his extra cash (roughly 100k) you can fully modify pretty much any vehicle
- You can wait until a point in the story where Michael's car is modified for you slightly and then adding the mods that were missed should pop the achievement for you
- You can wait and but the Los Santos Customs garage with Franklin, once he has enough money, then all mods will be free at that location
- You could go to GTA online and modify a vehicle there, money is much easier to come by online now-a-days, and you will also get a platinum award for doing this
Below is the checklist of things you would need to get, some vehicles don't have all of these but you just need to buy all you can for the particular vehicle you are in, and you only need to purchase the lowest level of the modification:
Armour
Breaks
Bumpers
Engine
Exhaust
Hood
Horn
Lights
Plate
Respray Primary
Spoiler
Suspension
Transmission
Turbo
Wheels
Wheel Colour
Wheel Accessories: Custom, Bulletproof tires and Smoke colour