Acebird,
There are internal ribs in the Drain Frame design and they are actuated by inserting a Flow Frame key into the drain hole and rotating the key 90 degrees. The cost of printing a Drain Frame will of course vary based on the type and brand of materials used to print the frame. Using natural PLA or PETG (both of which are generally considered food safe) you could print and assemble a deep version of the Drain Frame for less than forty dollars. A medium Drain Frame would be a little cheaper given that it uses less plastic than the deep version. As of the time of this reply, in the US, the cheapest you can purchase a Flow Frame for is $63.86 and that's only if you buy the "Classic 7" bundle for $447.00. If you didn't want to spend that much you could go as low as $259.00 and get the "Classic 3", but the unit cost there jumps to $86.34. Furthermore, you would have to modify your hives to accept the Flow Frames, the Drain Frame is the same size as a standard deep or medium frame, so no modifications would be necessary.
Little John,
Both the Drain Frame and the Third Comb designs have cells with a slope of 13 degrees. I'm happy to draw up the design of the fondant feeder you described. The Third Comb wall thickness is 0.4mm. Let me know what wall thickness you are thinking would be most suitable, also, the desired slope of the cells and I'll have the new design posted fairly quickly. If you don't have access to a 3D printer I'd be happy to print some frames and send them to you to see if they will work. Just let me know.