The Merengue can be bought from Total Motors car dealerships. It is a standard class vehicle and costs $43,125. After purchasing it, you can get it from the car dealer's garage or you use the "Car On Demand" app to have it delivered to you. Then, drive 4 km (2.5 miles) with this car to get the "Miniroadtrip!" achievement. Just drive it along a highway to quickly get it. You will get the achievement after stopping the vehicle, not while driving it.