So little info: There are 2 mount bikes in the game one for the Alliance( Mergineer's Chopper) and one for the Horde (Mechano-hog). The are almost identical so I won't talk about them separately.
For the mount you need 450 skill Engineer who knows the recipe.The materials are quite expensive:
12 x Titansteel bars
2 x Arctic fur
40 x Handful of Cobalt bolts
8 x Goblin-Machined piston
1 x Salvaged Iron Golem parts
1 x Elementium-plated Exhaust Pipe.
The last 3 must be purchased from Roxi Ramrocked at K3 in Storm Peaks . Their total coast is 12 500 gold.
If you are in a guild obtaining this mount won't be hard :P