Walmart. Fishing Isle. Utility trays.
If you are doing 1.5 inch cubes get the Flambeau 4007 trays. Should fit up to 1.5 inches snug. Can cut the little inserts out easy for them to hold the stem and cube in place. Six pack is only about $22. That is under $4 a shipper. They have four slots and can hold up to 8 clones depending on how you pack them. You can place clones on both sides of slots. Go on ebay and buy yourself some small battery leds. They run like $10 for 25. Also they ship and stock is usually solid when it comes to shipping these.
If you are doing bigger clones/bigger cubes (2 inch rockwool) get the Ozark 3700. Bigger slots and bigger case. Lower cost too. They are about $3 a case. They don't ship these but if you can find them in stock at stores, grab them up.
I did a write up on clone shippers once somewhere else. Will try to find the link.