Prices on a '70's model can vary fairly widely. One significant factor is whether the bass has had the electronics upgrade; most have not. Others are whether the power supply, cable, and case are included. And of course the condition of the bass is a factor. And if the bass has any non-Alembic modifications, it can significantly lower the value. Also, there is the market itself; sometimes there are more buyers than sellers, and sometimes more sellers than buyers. And it's been my observation that prices for these basses tend to increase over time. Off the top of my head, my guess is that currently a '70's model Series I with power supply, cable, and case but without the upgrade and in good condition may go for around $2,800. But that's just a guess and I could be way off in either direction.