I made a couple of rollfilm washers a number of years ago from stock plexi materials available at a local TAP Plastics store. The cost was about 20% of what they sell for at retail, as I recall. A print washer would be a bit more complex, but probably not overly so, if you have reasonable design and construction skills, along with the necessary tools. Woodworking hand tools are sufficent. Working plexi with power tools requires slow speeds to avoid melting when the objective is cutting.

While running water seems intuitively better, all of the discussion I've read suggests that soak and dump is just as good - assuming a repetition of at least five cycles during the alloted washing time, and good surface contact during all of that time. In trays, for example, you'd want to shuffle the stack frequently enough to ensure that all surfaces had good exposure to the water, and then dump and replace the water at the necessary time intervals. In truth, it's a chemical disbursal process, and running water really doesn't appear to add much - other than an unattended, semi-automated way of replacing the water.