You can get a microfilter for around $30-50 from Ebay (German made parts), then its a 3 minute job to change it yourself (6 screws). Then a 30 second job to reset the light.
Here is a link for resetting the service light yourself.
Its sounds like the Sevice Advisor / person is taking advantage of you.
http://3seriesblog.com/how-to-reset-...-3-series-e90/