This achievement may seem a little more daunting then it really is. The best way I've found is to build a cobblestone track starting at sea level (make sure you have enough room both length and height wise as the world is shrunk down a bit from PC) and build 10-12 blocks, then go up a step, 10-12 blocks then up a step and rinse and repeat until you've reached 500m (500 blocks as each block = 1 meter) and then ride it down. You can also join a friends world and do it through there. If you would like to use mine, send me a message on my Gamertag: Jocavs. I'll try to get to as many as possible. There is also a video below showing my run, and a little more detail on how to do it.
Edit #1 - I helped people for about 1-2 hours straight last night. If I haven't gotten to you yet, I'm going to hop back on every night for a few days. Thanks for being patient :)