There are 9 total jets you can purchase so you actually do not need to buy them all. I would highly suggest completely skipping the last jet (the Scorpion) because the jet directly before it (the Manta) is actually the highest rated jet in the game once fully upgraded. Here is a list of all the jets in the game and their cost to unlock...
Stingray - free / starting jet
Photon - $25,000
Striker - $35,000
Fireball - $48,000
Typhoon - $62,000
Lancer - $100,000
Shockwave - $170,000
Hamerhead - $240,000
Manta - $300,000
Scorpion - $375,000
The final tier of races in the game has the potential to earn up to $65,000 per first place win. Therefore, this achievement is much easier to earn after you have completed the career mode and unlocked all the tracks in the end.