Pay per click can be expensive and very competitive.  Competition will drive up the prices on a per click basis.  Find a legal referral directory that has great rankings and have them link directly to your webpage.  One you can try that has terrific Houston rankings: 

http://www.houston-texas-lawyers-attorneys-directory.com/houston-legal-services.htm
http://www.houston-texas-lawyers-attorneys-directory.com
http://www.legal-advice-library.info/
http://www.legal-advice-library.info/articles.htm
 
I work for an attorney that has several listings in this company's San Diego referral directory and we get a great deal of business from it:  http://www.sandiegolawyerforyou.com