The dealer could easily be outsourcing it and then again they could be simply charging you the hourly rate. I charge 1 hour for a straight alignment and 1.5 for a 4 wheel alignment. My brothers at the dealers charge 2 hours across the board at $100.00 per hour. If you can find an old timer that really knows Volvos and alignments both you will get what you pay for. If you get some green horn rookie who only knows what the machine tells him then you might not get what you want done.
Although you car came from the factory with toe adjustments only since then they have come up with alternatives to adjust both the camber and the caster. If you are having feathering problems you more than likely have an excessive toe condition going on. If it is truly feathering you should be able to look at it and see which direction it is feathering in. Is it feathering out or in? If it is out then your toe out is excessive and if it is feathering inwards then you are toed in. Mind you, it has to be pretty darn excessive to cause this wear pattern. As you described this "/\" would be a toed in condition and this "\/" would be toed out. Camber is just a matter of the top of the wheel being leaned in too far or out too far, if the wheel is straight up and down, at a right angle to the ground, the camber is said to be "zero". If it leans in or out it is either positive or negative. Caster is a little tougher to explain and I am not going to go into it here. Suffice to say though that camber and toe will cause wearing issues and caster is for the most part a pulling angle and not a wearing one.

You might want to go to your local dealer and see if they have any old codgers there that know how to align your car properly or go find yourself a front end shop that has been around forever and see if they have any resident codgers.

Good Luck,
Mark