What cost should I expect from a dealer or private repair facility or is it easy enough for me to do myself?
Spark Plug Replacement on 2004 BMW 530i
The estimator link at the repairpal home page says $240-$325 depending on the area you live in. From the size of estimate I would be tempted to say that without the knowledge and correct tools that it may be beyond your ability. Typically plug replacement is maintenance and if owner has to ask if can do then without knowing your tool stash and mechanical capabilities then I would say no. Gaining access can be time consuming and confusing.
Cost is about $300 if we do it, but with over 30 computers on that car, you have to know what you are doing using scanners to recalibrate the PCM, or main computer.