air pump

I have decided to add a small air pump to my pond. This is I believe simply
peace of mind insurance, so I want it to be cheap insurance. I could use
some suggestions about how small/cheap I can use and still be providing
benefit. I don't even know how air pumps are rated but will doubling the
output double the 'benefit'. The air stone? Round, big, 2 inch, foot long,
small bubbles???? I have been unable to find hardly even any opinions about
what to actually use, once I have opted for the air stone method. Well
Ingrid mentioned an absolutely, positively setup but much more than I want
to spend.
Thanxx
Bill Brister - Austin, Texas