To tell the truth, some users at Armadaboard take $150 a month. 
Surely in case of an advanced payment for 3-6 months there is a discount.
Also you can place up to 6 ad spots at your signature. In this case the price is also lesser ($50-60 each).
Well, then you should create a thread to sell your signature space at their forum instead. Don't expect to find someone in this forum that is willing to rent your signature space for that price. Anyway, good luck. Surely in case of an advanced payment for 3-6 months there is a discount.Also you can place up to 6 ad spots at your signature. In this case the price is also lesser ($50-60 each).