To net this achievement you'll need to keep winning races until you have $25,000 in game credits. Once you do, at the Race Select screen, hit Up on your left stick to highlight the button in the top left of your screen, that has the name and Index of your current jet-bike. Press A on it.
Then highlight Buy New, hit A. If you saved up the minimum $25,000 you will be able to afford the Photon. Highlight it, or any other bike you can afford, and press Up on your left stick, this highlights the Buy button. Hit A, and the bike, plus achievement, is yours :)
Keep repeating this, buying 4 then 8 water-bikes, to net you the Enthusiast and Collector achievements, earning you 30 & 45G's respectively. It'll take a while though, and a lot of money :)