KeepAlive works awesome. Been using them for Redfish Tournaments and have never lost a fish. Highly recomend. They might be more exspensive than a regular aeorater but much less than a full oxygen system.
You cannot beat an oxygen system. Aerators can infuse only a tiny fraction of the much needed oxygen, simply because it uses atmospheric gas which is only about 1/5 oxygen.
Water has a finite ability to absorb gas... once it is saturated, that's it... no mas! No mas good gas or bad gas.
The cash outlay can run between $200 and $450 depending how large and elaborate a system you purchase. If you understand welding gas, regulators and diffusers and have cheap access to proper components you might get it done for about $100. Be advised though that an improperly designed system can be dangerous.
Easiest and simplest I've seen is the FishFlO2. It uses Bernzo-matic disposable oxygen cylinders and comes with built in regulator, hose, and a good diffuser. Price is around $200 and it will outperform any bubbler or aerator you care to compare it to. A cylinder of oxygen retails for about $10 and will get you through several days of operation.
I have been using the KeepAlive system for a few years now and have been very happy so far, the other day we had a couple of quarts of shrimp last from just before lunch until a little after dark and the shrimp were just as lively as when they were first put in the livewell.
I have been using the Keepalive for a few years. The results: I have about a ..05 % mortality rate. Shrimp and baitfish very rarely die in my converted ice chest. It works as good or better than my buddies who use oxygen. This is from actual results, not theory! No need to spend money on the oxygen system with the www.keep-alive.net system available.