Advertisers being cheap?

It's come to my attention recently that advertising is becoming increasingly harder to sell than ever before, perhaps this is due to the summer season or is it due to the prices i'm offering? (even though they are highly competitive and offer a much better deal than alot of similar forums).

My question is, are advertisers just being cheap? I'm only charging $50 for a months worth of advertising but in many peoples eyes this is too much! What do people honestly expect to pay?