Midnight Club: Los Angeles

After you have beaten the city champ (unlocked about half way throught the career) you will be asked by Karol to buy a 50% stake in his garages. To do this you must raise $1,000,000 dollars in total. After you have completed this mission the achievement will unlock. Now you can go and see Karol to beat the career. I would make this your priority over beating vehicle champs because once you've paid Karol all the cars and upgrades are free (expect unlock-only).
To get $1mil I started by doing some more of my missions, for example the tournaments and beating some of the kingpins (unlocked cars can be sold for quite a bit). I also sold all my vehicle except the one I use the most (the Ninja bike). From there I just did 'Welcome to Hollywood' in arcade mode. It is the shortest race, and with 7 opponents, traffic off and on hardest difficulty you can get about $5,400 every race.

I didn't really get on with this game and didn't beat the city champ but i saw that this cheevo wasn't to hard to get quite early in the game.

I used the Deliver missions to obtain this in a few hours. I found that on easy i got between 10k and 14k every 3 mins with great ease, if i thought that the delivery was to far then i would just select next delivery, Also no cops to worry about or slow you down between races.

im sorry but im not to sure when the first delivery mission opens up but it is optained at the garage you start at. If you can't choose the difficulty at first then go back again.

This achievment isn't very difficult to get, just keep doing wager races so you get a good amount of cash for easy racing. I do suggest until the end of the game to get this achievment after you beat the city champ and Karol offers you the partnership and tells you to raise the $1million. Its beneficial for you as the player because when you give Karol the money you will be able to obtain everything in the garage for free, cars, tuning upgrades, parts, everything. This will be a big help for achievments that require you to beat specific vehicle type champions.

Once you defeat Booke, you will be called by Karol to have $1,000,000 in order to have a partnership with him in his garages, which makes all vehicles and parts free.

You may want to avoid buying any vehicles and just use the ones you win from the tournaments, pink slips and time trials, such as the Dodge Challenger Concept DUB Edition, Mercedes-Benz S600 DUB Edition, Lamborghini Murcielago Roadster DUB Edition, Datsun 280Z, Mitsubishi Lancer Evolution IX MR, Chevrolet Camaro RS SS,
and Mitsubishi Eclipse GSX.

Once you win the Downtown DUB Tournament on Hard Difficulty for the Lamborghini Murciélago Roadster DUB Edition, you should use the said car for the rest of the game, and just only spend $58,880 to upgrade it after unlocking Level 2 upgrades for Group 4 vehicles.

Despite being able to complete every mission with only the prize vehicles, the motorcycle missions are the only ones that require buying a vehicle, in this case, once Andrew tells you to get practice on a motorcycle, you have to buy one, with either the Ducati 1098R (from the South Central Vehicle Pack 2) or the Kawasaki Ninja ZX-14 being the recommended bikes, due to their exceptional stats and low price.

It is also not recommended to buy any visual upgrades (except for those that are free including the South Central rims) until you buy the garage for $1,000,000 in the endgame, just use the money to buy performance upgrades for the cars you win via the said missions.

The Delivery missions in both garages are good ways to earn money, as these have high payments, assuming you deliver the car fast in mint condition. Just set the difficulty to Easiest (Green) or Medium (Yellow), then deliver the car on time with less than the target visual damage and you will get paid. You may want to do the deliveries until you unlock both delivery-related achievements.

You can also do Wager Races to increase your funds. However, if you lose or restart a Wager race, your bet will be paid to the opponent.

After getting the call from Karol following Booke's defeat, sell your most expensive vehicles to quickly get to $1,000,000. The Mercedes-Benz S 600 and Lamborghini Murcielago's DUB Editions fetches the most value when sold, so win their respective DUB Tournaments on hard difficulty before doing the $1,000,000 garage deal, then sell them after becoming the City Champ as these cars are worth a lot of cash when sold.

To Do This, You Need To Get The Kawasaki Ninja.

By Doing So, It Probably Won’t Want You To Waste Your Money. Then, Do About 500 Races, You Might Get It Early Because You Have A Lot Of Money.