After having selected nearly every part needed to buld the automatic feeders, I decided to do a cost analysis to make sure I'm still in the right path with the project.
Here's the BOM for one 8 channel feeder controller:
All the prices were taken form authorized electronics distributors, and I estimate the feeder PCB to cost about $3 USD.
The motors needed for the feeder are about $1.5 each in single quantities, and each feeder uses about 75 grams of PLA filament. The laser cut tape sprocket adds another $5. Taking all this into account, the mechanical parts for a single feeder amount to $9.5.
In total, we are now at $14 USD. I still need to add the cost for the cables and the final quadrature encoder electronics and a few fasteners, but I feel that a cost of less than $20 in parts is very attainable. Also, this analysis does not take into account the volume pricing of any part, meaning that when fabricated en masse the cost will be even better.