lens upgrade help

[supermoto]

I am very new to this, but am enjoying my Canon Rebel XTi for shooting mostly mountain bike jumping. I think I would like to upgrade my lens to something wider angle and faster, as I am usually close to my subject and often shoot in low light. I am currently using the EFS 18-55mm f/3.5-5.6 that came with the camera. Can you make a suggestion?

[SmartWombat]

From this shot it looks plenty wide enough for me.
Wide than 18mm ? I use the Canon EF-S 10-22 but it's expensive.
A larger aperture faster lens is going to cost a lot, so how big is your budget?