I checked on the rainwater harvesting system at the Master Gardeners Test Garden and this is what I found: According to Micah Meyer, the Horticulture Agri-Life agent, the system wasn't expensive.
"We had to buy the gutters, pvc pipe, & glue. The rain barrels were donated. I think we spent around $100 dollars on it. You should be able to find a rain barrel for under $50 or sometimes free. Depending on your current gutter system, you may not have to buy anything extra at all. I would imagine that most people could install a simple rainfall collection system for around $50 to $150. Its just a matter of how fancy you want it to be," Micah said.