more CO2 questions

George listed the below items.

 > $75-100 for a 5-20 pound tank (new, cheaper if you buy used)
 > $40-60 for a regulator with high and low pressure gauges
 > $10-35 for a good fine control valve
 > $10 for some kind of DIY reactor
 > - ----
 > $135-205.

Now what is DIY reactor?  Cannot I just bubble the CO2 through an air stone
or is that really ineffecient?  Also what about the comercial CO2 systems
like Tetra makes, are they any good or just plain unbelievably expensive?

Then in another article George mentioned his WWW page.  What is the address
that I can pull it up on George?