Once you get to a point where you produce something f value, you won't have to ask, you will know.
This is not at all true...every thing has value and most artists do not know how to put a price on a piece of artwork. You are a bit harsh and harsh is not always a bad thing but when it comes down to it this piece does have value even though like you said it may not appear finished but there is a market for it.
First question would be how long did it take to do this piece, second what is the format. Who are you marketing and what medium. Also I would look on the internet to see what that style of art is going for from artists that are in the same level you are.
For being a new artist and for being what the piece is I would put a price of $75 on it and see what bites. Although this piece you have to realize will go to someone who is into this kind of art work and more than likely will not sale right away.
Another thing presentation is everything, present the piece mounted or in a frame and it will have a better appeal.
Until you get you name out there and have some sales under your belt it will be very disheartening at first, plug at it and if you see that none of your art is selling, you may want to reconsider your subject matter. Hope this helps!