Dane,
A '74 Series I shorty is certainly a high demand item. Do you know if the body is the large standard body or is it the smaller one? Do you have the DS5 (blue box) and the cable? Case?
All of those things will factor into the equation in terms of price and certainly any interested buyer would want to know about the condition of the bass- any non-local buyer is going to need pictures at some point probably.
In terms of price- Series basses in good condition are almost always above the $3000 mark and with the power supply, case and cable, that number definitely goes up. The fact that it's an early serial number would certainly make it more desirable for some buyers. There will be others who chime in here shortly, but I'm guessing you will certainly be at or above the $4000 mark if the bass is in good condition- possibly much higher depending on the buyer and demand.
Pictures would definitely help.