I have a 2004 Toyota Corolla

I have a 2004 Toyota Corolla. The belt on the left side of the engines vibrates while the engine is cold. I was told that the belt tensioner assembly probably needs replacement. I check with a few dealers and a few shops, but was told it would be around $450 to replace (including a new belt). I can buy the parts myself for around $150. Is this something I can do myself?