In jurisdictions in which there's a large imbalance between the parties the general election is a foregone conclusion; the primary of the dominant party becomes the real election. Primaries still have lower turnout and feature candidates with less name recognition, so the potential impact of money is quite high.

Not easy and effective post election .

The candidate doesn't own you anything and cannot receive donations directly anymore. Thus you get to pull the corruption, illegal, or indirect, less effective, cards.

Supporting the candidate to get him elected is much different.

Maybe it's a sign that your "pennies on the dollar" theory needs some work?