There are two ways of getting this achievement. 1 - Inexpensive and possibly time consuming & 2 - Instant and extremely expensive.
1 - You can go to the Slot Machines (Located above the right hand staircase upon entry to the Casino) and play on the TDU2 Life Machine to try and win the car by winning the jackpot, which will also result in winning $1,000,000.
2 - You can simply buy the car in the lobby, this is confirmed to unlock the achievement. The car costs $1,000,000 Casino chips, which translates into $2,000,000 outside the Casino.