The downspout of the eaves trough runs from the roof right down to ground level. You ll need to shorten it enough to get the rain barrel underneath the spout. Most downspouts are a series of aluminum tubes with tapered ends, tucked one into the other and nailed or screwed onto the building with brackets. A basic plastic barrel made for shipping can be scored at a garage sale for five bucks or so but again, know the past lives of your barrel, and be aware that you ll be watering your plants by hand-filling a bucket or watering can from the top of the barrel. If you re having trouble finding a cheap barrel, try getting in touch with a local environmental group, or even contact a food distributor or shipping company and ask them.
Affordable barrels are out there.
Many environmental groups and cities across sell rain barrels at subsidized prices, in much the same way as they offer compost bins for sale.