I was in the same predicament as you a few months ago (see "Will This Pump Work?") and currently my pond is a-bubblin' away for under $60.
I bought the GAST 1532pump for $40- it's 1.5 CFM, good for a small pond:
CHEAP and GOOD! I used 5/8" garden hose to go from the pump to my pond.
And this diffuser:
Also, CHEEP and GOOD! Yes, it can be done for under $60, it works great too, big time surface boil in 15' of water.
