Target has the 6′ Unlit Alberta Spruce Christmas Tree for only $15.00! (Reg. $30.00) This is the cheapest I have ever seen on a tree this size! You will need to choose in-store pickup, as it is not available to ship.
This tree is not pre-lit, however you can grab 100 mini Christmas lights for only $1.88! I just posted about this from Home Depot!