Try the content network. Google Serp isn't the only game in town online. Consider Facebook, or other ad networks.
Google prices are getting high because everyone is flocking to it. The serps will reach a saturation point unless the number of searcher grow or the competition shrinks.
Consider this. Find your best Keywords. Find the sites that rank the best, and have good Quality. Negotiate A direct ad on their sites or maybe even see if it's feasible to buy the sites. Also consider the first second and third site.
Use the Sites to get traffic.