According to the 1973 catalog the 576 was $2600 (no options included). The 577 isn't listed in that year. The 1976 catalog lists a non-storage 577 with no test fixture for $2300, the storage version for $2625 and the base test fixture was listed at $500.
I don't know how those prices related to on the street prices. I worked at a very large company and we routinely got 30% off list price at purchase time. It was also rumored that the company got a large kickback at the end of the year based on total sales. The kickback was rumored to be another 20-30%.