I did something like this with job ads on my main site. I was charging $199 for 30 days, but wanted to get out of the contract with the people who ran the board by stopping new ads. So I put the price up to $499 but I still got a few sales. So I put it up to $899. A day later, I got a sale.. at $899!

Since then, the board has had better traffic so I've stuck with the provider and now charge $249 for 60 days. Seems a good middle point between quantity and money.