When you try to rank for a new keyword, it's always easier to build on an existing "platform of authority" than trying to build a new site from scratch. An easy way to do this is to buy old domains that already have links pointing to them.
The cheapest way to get old domains is through Godaddy. Omegaweb explains:
When a domain name expires on GoDaddy (note that this is specific to GoDaddy, other registrars do it differently), they make attempts to contact the owner to renew the domain. If the owner never answers the emails after 26 days, GoDaddy will list the domain name in their "Expiring" category on the Auctions page. If nobody bids on the domain in the expiring bin, then they move it to the closeout category. To purchase a closeout domain, you do not have to pay the $5 a year membership, and most domain names are $10-20. If nobody bids on it in the closeout bin, it is officially an expired domain name and is available for anyone to register.