The Web vs. other forms of advertising...

I met with an attorney last week who is considering upping his advertising budget. He is considering either an AdWords campaign or a billboard. His area of practice is mainly ADR and Mediation but also practices litigation. He mentioned that the billboard that he likes is available at the corner of 59 right where it meets Spur 527 from downtown. He thinks he can get a bargain because its been open for a while. The "bargain" is $1500 a month...
My question was the following, "Sir, would it be more effective to have a billboard where people who are leaving downtown towards 59 who MAY need a Mediation Attorney can see it OR an ad on the two most searched websites on the planet when someone searches for 'mediation Houston' or 'ADR Lawyer?'" Seems like a no-brainer to me.
I'm talking about highly qualified traffic from Google and Yahoo. The only clicks you are going to get are from relevant searches. No billboard, newspaper ad, radio spot or any other form of advertising can provide that level of QUALIFICATION.
Here is the best part - the budget estimate on what his campaign would cost??? $700 a month. His ad would show up all over the country on Google for half the price of the BB on a SPUR 527 and Highway 59.
He's thinking about it...
There is a saying in poker - Think long, think wrong.