If you want an actual bin, you can buy those, or you can knock up a wooden structure, minimum size 3 x 3 x 3 feet, leave open at the bottom onto soil, and one side will need removable door near the bottom to extract ready to use compost.

If you visit the waste aware web site you might be able to buy the bin type very cheaply some councils subsidise them I got mine for £10 and they had smaller ones for £8

Pick up 4 pallets from your local builders merchants (free). Find 8 pieces of wire, tie 2 on each corner, to make a cube with an open top, no bottom. Line with compost bags, cut open, black side to the wood inside, secure with drawing pins. Fill up with a 4inch layer of whatever you are composting, adding some old compost or horse manure between each layer. If you want a turning area, wire on 3 more pellets. When composted or if turning, open one side, hinge back the pallet.