It's worth what anyone will pay. Brass lamps are often worth more than scrap value. Try listing it on craigs. Read the Sunday junk mail inserts and look at what they charge for new lamps nowdays, then list for 1/3rd to 14th the new cost of a similar one. And often they are not even brass.

I've got brass lamps sitting all over in here. Too nice to scrap. Some I found have already had the cords chopped. Need to do some rewiring.