I did test various price points to get a sense of the response, and it was done mostly via craigslist.
One caveat: On one park i wasn't getting as strong a response from Craigslist as i would have liked, but still went forward with the purchase. Since then, I have found directional signs ($5 at Lowes/Home Depot) have pulled much better than Craigslist for that particular park. I would spend a little $$ and put some signs on the main streets around the park you're evaluating to get a sense of how many calls are generated. In other words, it's easy and simple to do online ads, but dig a little deeper.