That's about the going price for any tune-up for sewing machines. They check the timing, etc...but I still think it's expensive. I found some instructions on You Tube on oiling my Bernina...and there is also online manuals as well. I clean out the fuzz on mine after every bobbin change and oil it on a regular basis. I sew quilts and things quite often, so as long as she runs smoothly, I skip the yearly mainenance. Like going to the Honda dealer and wanting to charge me $60 to change a cabin air filter when I can buy them for $20 and takes 5 minutes of my time to do.
Go to a quilt/fabric shop and talk to some of the ladies there. They may have the same model or at least help you out. You don't need to go to one that sells your brand, either.
The dealer was really not making an odd comment. Many of these brands now will lose warrenty, etc.. if you take the machine to a non-certified brand named dealer. It's a big racket. Someone should do an expose on these companies. They are now made either in China, Japan or Taiwan...come over on the same big boat, get rattled and jiggled throwing off the timing and then have to be serviced before buying...and make sure it is before buying otherwise you have a lemon.
You can also go into some of the sewing or quilting forums and ask there.
Just a side note: check the direction of your bobbin. Some turn cockwise, and some machines require counterclockwise. If it's in the case going in the wrong direction, your bottom thread will get big loops or messed up like a rats nest. The timing may also be off as well.