You can use a variety of materials to construct raised beds. Most beds are made of wood.
However, pavers make great edging material that lasts virtually forever, and this works great when edging up to a concrete path. A simple paver costs between 40 cents and $2 at Home Depot(depending on size). You will need about 30-60 pavers (depending on size) to build one raised garden bed. Here is a good example of such inexpensive paver: Pavestone Holland 4 in. x 8 in. Concrete Paver, 39 cents http://goo.gl/F2OEF
Read more How to build a raised garden bed with pavers at Doctor's Garden.