YOU CAN DO IT!!

If your only concern is cost, then as Burton mentioned you will want to include the cost of any tools you may need (crank puller for one to service the BB) in your calculation. However, I prefer to do the work myself even if it doesn't necessarily save me any money. I consider the knowledge of what I learn to hold more value than a few dollars I may save by letting someone else do my work - but this applies to all things in my life and I realize it does not hold true for everyone.