FWIW, we would probably charge somewhere around $225-250 to diagnose the
unit and replace the parts you mention. Transformers usually do not fail
on their own. Usually a short in the 24volt side is the cause. The short
is usually either in the wiring going to the a/c, or the homeowner
accidentally shorting them attempting a DIY. I know that cost of living
in Ca. is much higher than here, but from what you describe, it sounds
like you paid about twice as much as the repairs should have been.
Larry