Go buy a corrugated plastic PVC roof panel for like $20, and cut a section as long as you need. In a 3x3, you'll only need a few feet or so, and its usually like 26" wide, which is wide enough for a few pots.
Using up the whole panel, you can double or triple up layers of thickness to make it stronger, with less framing underneath if you wanted.
Make a sloped table like frame for your panel to sit on (the water can only go 1 way down the grooves, and it elevates pots at the same time), so it runs off into a small wide/low tote, or even a small section of rain gutter, just like a roof does. Put a bilge or condensate type pump in the run off catchment container, whatever it is you use.Keep it all as low as possible. Simple!
I wouldn't pay a ridiculous amount just to ship some little low tide 3x3 flood tray either, that probably isn't even wrapped up or anything, and all scratched or cracked from shipping it.