There's more bang for your buck in local races:

If you’re a typical donor of the $25, $100, or even $5000 variety, your money is just a drop in the ocean of the hundreds of millions of dollars that both sides are going to spend on the presidential election. But more importantly, what we know about voter behavior suggests that money is least important in presidential (general) elections. Money matters more in nomination fights — where the candidates share a party label — than in general elections, where most voters will use the party label as a powerful cue. Moreover, voters will pay less attention to information they hear through paid advertising when there is plenty of other information available, as is the case with high-profile presidential elections. Add it all up, and your money just matters more — a lot more — in lower profile contests.