Audio Research SP3-a1

 ARC does not charge excessively for repairs. What did they say was wrong with it? A unit this old may have a number of issues but ARC will go through it with a fine tooth comb. It is worth the cost.

 Has your unit been "modified"? If so ARC will insist on removing the "modifications" before it can be repaired. This is a classic piece, I would not let just anyone work on it.

My SP3-a1 is a stock unit and they want around $1800.00 to rebuild the power supply., then they were going to look at the audio section.They also offer an up grade to the SP3 for $2900.00 plus tubes (no shipping)!   Maybe I'm just out of touch with things cost today !                                                                                              Thanks

Unless this unit has sentimental value, I’d put it in the closet and look for a clean ARC LS-2B with remote ($1000 to $1500).
BTW, $2900 today was worth $900 in 1980. Also, there are three for sale here as I type.