I have a couple of new in box Million Air MA-600 Air Pumps. $15 ea or 2 for $25
Here's a description
A high quality twin valve aquarium air pump at a very low price! This dual outlet pump is designed for use in tanks up to 60 gallons and larger in volume, producing up to 2666 cc/m per side. A built-in variable control rheostat allows the air pressure produced to be easily raised or lowered. Excellent for running air stones, diffusers, ornaments, corner filters, etc. Each pump measures approximately 5-1/2" x 2-3/4" x 2-3/4"H. Operates on 120V - 60 Hz household current only. Strong and Reliable! Super Performance! High Output! Safe and Quiet Operation!