Are the lenses -C lenses, or just Mamiya Sekor? the -C lenses are multicoated and worth more.
Incidentally, I just sold a nice (probably 8.5/10 condition 50mm -C lens for $220). Depending on condition, they sell for $150-250. Non-C lenses are worth $50-70 less. The 90 and 127 lenses are worth $80-125 for the -C lenses, depending upon condition, non-C lenses are worth $20-40 less.
RB67 Pro bodies sell really cheaply nowadays. Like $100 or less with WL finder and RB adapter. Pro-S backs, $50-75 depending upon condition.
For reference, a typical complete RB67 setup with body, WL finder back, and 90 or 127mm lens tend to go for $200-250 tops nowadays on ebay.