Window Advertising - Help

[avo70]

HI there

I run a shop and post office, and have been approached by an estate agent to who wants to rent out one of my windows to advertise propertys within the local area.

Window is 46" x 54" if that matters.

My question is, how much should i charge for the privalige, i have absolutely no idea what to charge.

Any help would be greatly recieved.