There is no simple formula as it will vary from chip to chip. For instance there might be 100 know examples of a chip but 98 are worn, in which case condition would increase value by many times. If for the same chip, half the known examples are Unc., there might be very little difference. Campiglia and Wells gives values in Avg. SU and New but does not cover as many varieties of chips as TCR so you really need both books. For your chip C&W gives values of $50 Avg., $75 SU, and $120 New. Hope this helps.