Can anyone suggest/cross-reference the part number for my circuit board? The model number for the unit is 48SS018-060. Thanks.

No expert, but close enough in the business to believe that Carrier is a good brand but very protective of their product. I think your best bet is to find a dealer.

I had a Carrier repair guy out here Tuesday and he quoted me $550 for the part and installation. That's crazy!
I figured I could get the part for less than $250 and put it in myself.

I wish you luck in finding the part. You may need to find a dishonest or disgruntled Carrier technician to provide the part via black market. Along with the cost of the part, the $550.00 also represents the tech time and training the cost of overhead for his benefits, the cost and overhead of the truck, office, warehouse,etc. and a reasonable profit.

The advantage of using certain brand names of equipment sometimes is a disadvantage for repairs due to the proprietary components used to build these systems.