Stocked GarageG 20

You can buy whichever three vehicles you like to unlock this achievement, but if you’re saving your money for weapons/attachments and want to get this done cheaply, you can. Some of the cheapest vehicles in the game are:

Funaki J-170 (the jet ski) - $1,000
Funaki E-716 (the ATV) - $1,100
2004 Hayai ZIP-R (the hatchback) - $1,125
2009 Hierarch FT-100 (the tractor) - $1,150
Salacia RHIB-Z200 (the unarmed boat) - $1,150
2008 Kimberlite Darrala (the 4-door sedan) - $1,200

So you have a few options if you want this achievement for $3,225 to $3,500. Note that you don’t need to pay for any custom paint or anything, just the vehicles.