Depends on whether you can do the work yourself or not - if you can, the cheapest is usually crazy paving, which means you find a supplier of broken paving, they dump it outside your house, and in the meantime, you've cleared the garden, excavated to a depth of 2 inches minmum, preferably 4, levelled off, ordered builder's sand and some concrete, make a lean, dry mix of the two and spread over the area 2 inches deep, then arrange the stones on top and point between them with mortar mix, holding all in place with shuttering round the edges with sufficient space to fill with concrete to hold it all firm, unless its butted up against a wall.