What to use as a drip pan?

Okay so i am having a bit of trouble finding drip pans big enough to accommodate my 5 gallon planters, i need something at least 14 1/2 x 14 1/2 inch's, i have been trying to figure out something that will work for a decent price for quite some time and have come up with nothing, not only have i not found any thing that will work for a decent price but i haven't been able to find anything big enough period. Any ideas or suggestions would be greatly appreciated...

Try the auto parts store for the drip pans for DIY oil changes.

The round ones fit a 5 gallon bucket exactly, like the homer buckets from HD and cost ~$3 each.

They have rectangular ones also, but I've never measured them.

Wet

You can take a heavy plastic like visqueen or Panda film and fold the edges up to make catch trays.