Overcharged for McIntosh Service?

I recently took my McIntosh MA6100 to a local repair shop that is an authorized Mac service site as the right channel was dead. I had to leave a $40 deposit to cover the cost of the diagnostic to be applied to the repair bill should I choose to have it fixed. I was told I would receive an estimate by phone before the work was to be done. Several weeks passed and no call. I called them yesterday and was told 2 fuses, 2 output transistors and two driver transistors need replacing for a total of $270 (89.00 parts and 180.00 labor). When I questioned the cost I was told the work had already been done. They assumed since it was a McIntosh I wouldn't balk at the cost so they didn't bother to call with an estimate. When I voiced my concern as to the high repair cost and the lack of an estimate I was told my only recourse was to have them open the Mac back up put the old parts back in and forfeit the $40 deposit. Also I was told that now when I turn it on there would be a hum during power up which dissipates in a few seconds which it didn't do before. In order to fix that it would be even more money.
I got a real bad feeling and just wanted to get my amp back from this guy so I wrote a check for the balance and picked it up. The right channel does work and the hum although I really don't recall it before the repair does stop in a few seconds after powering up. In addition to the obvious concerns regarding the lack of an estimate and the hum I question the validity of $180 for labor. Looking back I am tempted to stop payment on the check and negotiate with this guy offering to pay for the parts and split the labor which totals $180. Am I being unreasonable?