for a cheap alternative, and an easy hook-up if your bait tank is equipped with an Oxygen infuser pump (keepalive) is the Oxygen (control valve) and the convenient Oxygen bottles available at any hardware store (less than $10).
The pump normally "Atomizes" outsize air into your bait tank. and quickly dissolves in the water. so there no need for an air stone that wastes O2 and allows the Oxgen/air to bumble up to the surface and waste into the outside air (which can be a hazard if a flame is in the area- just makes things burn faster).
I found the control valve in a kit with MAPP gas (Bernomatic Cutting, Welding, and Brazing Torch Kit (WK5500OX) from ACE Hardware ($60) ). Remove the control valve, and hook it up to the hose running to your Keepalive Oxgen infuser pump.
Then freeze salt (non-iodized salt is what I prefer) water in a 2 liter bottle, and drop those into the bait tank (if you are not going to change out the water) to keep it cool. However the temperatures are now cool enough that I'm able to keep shad alive (still adding shad saver to the bait tank) without the need for exchanging water, or adding ice bottles (as long as I don't over crowd with larger gizzards).