Cheap, because it can be done entirely on a computer using original material that’s either public domain or fair use. Generic, because with minor variations it’s suitable for many, many different races. What’s needed is image morphing software, which is available cheaply (by political campaign standards) or free from all over.
Start with an image of the Democratic candidate, and with one of either Nancy Pelosi or Harry Reid (as appropriate for House or Senate races) in full musth. As the image slowly morphs from that of the local candidate to that of the national “leader”, the voice-over intones:
[Candidate] voted for [strike any not appropriate] the stimulus that failed and left us in debt, for the takeover of health care by Government bureaucrats, for higher energy prices and limited access to energy, and… [fill in blanks]. When you vote for [Candidate] you aren’t voting for a representative of your interests, you’ve voting for the Democratic Party’s agenda. A vote for [Candidate] is a vote for [Nancy Pelosi | Harry Reid], and for higher taxes, bigger debts, and less freedom.
[morph completes at this point]
[change to picture of Republican candidate]
[Candidate] will represent you, not the Democratic Party’s agenda. Vote [Candidate] for relief from ever-growing taxes, debt, and Government interference in your life.
Modifications are of course necessary and desirable; I’m not a scriptwriter. The point is, one basic ad layout will do for most races. Several people have noticed that Obamacare, “stimulus”, and Barack Obama are almost embarrassingly missing from Democratic candidates’ advertising message. They’re trying hard to run away from their own sorry records. Don’t let them succeed.