After checking my stats in many places I have determined that while this is a unique venue, the price increase is not worth it because I get more traffic exposure in other places that are essentially free.

Had this been the old rate from last month, I’d do it again because I was still in the process of evaluating the performance based on the old price.

I do believe you should consider subscription-based with a discount for multiple months/years.

Lastly be good to these people who made this site. Count up how many referrals they brought here and consider the idea that if a member brought you 50 or 100 new people for example, either give them free lifetime ads, previous rate, or a discounted rate.

I know with a lot of marketing sites the price increases as the membership grows due to many factors – operating costs, time it takes to admin, upgrade features, etc. BUT some of them allow you to lock in your subscription rate before a certain date or membership milestone. Which could be just what you may need to keep your current members happy but apply the new rates to new members from here on out.

Thinking aloud:

Have you considered making the first month of advertising cheaper, so people can start up?

I’ve seen in the blogging community that clicking/dropping at other sites is considered an investment, maybe not in time, but in money.
So that means that there’s a group that has to invest more money ànd more work to see a return.

Interesting is too that on other programs people pay to have no ads on their site.
Here they would pay for visitors to their site, but by having no addtional adgitize ads, the surfers will ignore them as they get to know that visiting their sites does interrupt their rythm of visiting.