A good place to get cheap equipment such as this are those government auctions. Things seized in raids or due to backed taxes and such are normally cheap and if you need something fast, this can be your place.
Another place that I have found for everything, not just large equipment, is
Public Surplus: Government Surplus Auctions. This is a site that many government agencies sell off items they no longer need. You might be able to pick up some cheap items in your area.