There's a trap called the Squirrelinator that looks interesting, and they have them for $30 (usually closer to $60) at my local Tractor Supply, but all the glowing testimonials are for catching ground squirrels, and I'm having trouble with tree squirrels. Maybe it works for them too, I dunno.
But I do still have the Havahart trap, I should set it up and start drowning them one at a time while I'm figuring out a higher-volume solution. Also the box trap won't upset the wife or neighbors, they don't have to know about the drowning part.