Very easily done at home, and for a lot less than $160. It is very very easy. If you cannot find a DIY anywhere online, come back and let us know. I can probably type up a good step-by-step, but not right now -- I am at work.
Check our DIY section here, and also try www.bimmerdiy.com
, if necessary. Many say you need to remove the engine fan -- not true. Do not follow such procedures.
You will need a 17mm socket wrench (to release the tensioner on the belt), and -- I think -- a 10mm wrench (to remove the aribox, which will make it a lot easier to do). I believe those are the only tools you need.
Good luck. I;ll check back tonight