About 600 people packed on to the Machinery Auctioneers lot on the outskirts of San Antonio, Texas, last week to pick up some of the pieces shaken loose by the oil crash. Trucks, trailers, earth movers and other machines used in the nearby Eagle Ford shale formation were sold at rock-bottom prices. One lucky bargain hunter was able to pick up a flatbed truck for moving drilling rigs — worth about $400,000 new — for just $65,000. Since the decline in oil prices began in mid-2014, activity in the Eagle Ford, one of the heartlands of the shale revolution, has slowed sharply. The number of rigs drilling for oil has dropped from a peak of 214 to 37, and businesses, from small “mom and pop” service providers to venture capital companies, are trying to offload unused equipment.