Where/when do you all find the best deals for planter boxes?

I’m thinking about buying a couple for my balcony. I’ve checked craigslist and let go, but there’s really nothing being offered beyond small, individual planters.

Where/when should I be looking for the best deals? Resin is much cheaper than natural wood. Is this something you’d recommend? What’s the price range I should be able to buy unreservedly?

Thanks for any help.