I have no idea whether TAP is treating you with respect or whether the shipping cost is reasonable, but your obvious frustration comes across. From other posts it seems you've had the amp since at least 2011 and you state that it sounds wonderful. Maybe a better way to look at this is to spread the repair cost over the life of the amplifier and accept that wonderful sounding state of the art performance really does cost hundreds, if not thousands, of dollars per year in upkeep costs.
Please let us know the outcome.