Jim's idea is a good one, but the 11 1/2" Verito converts to a 20", not a 24", when the rear cell is used alone. Should still have plenty of coverage for 11x14, but it isn't going to meet the "inexpensive" part of your criteria.

I wonder how your Artar would work if you unscrewed the cells a few turns to increase the spacing. This is essentially how some of the variable soft focus lenses work, but they're probably different formulas than what an Artar is. Still, it would cost little to find out. Just don't unscrew the cells so far that they fall out!