Cheap trays for planting might be an option? I get long black trays like this for a buck or so at Lowes. They're not very thick/sturdy plastic, however, and don't stand up to much if you're washing/moving them a whole lot (at least for holding water!)
There ARE heavy duty trays, but you can't find them at Lowes and the like. They run around $12 or so. Look for "permanest" trays. You'll probably find them from african violet growing sites or maybe even hydroponics sites. Generally they're 11x22x2.5 inches.
Other options I could think of to be more environmentally conscious would be to maybe scavenge an old fiberglass tub, and use a saw to cut out the "tub" part, about 3 inches from the base. Then you'd have a short basin AND a drain that you could just plug. In our city there's a place called Construction Junction where people sell/drop off old deconstruction materials - toilets, tubs, windows, old/broken tiles, etc. This would be a lot of work, but I bet you could get a pretty good result from it. Just please wear a mask!
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