My first thought would be to ask, do you actually meen a raised bed ?
I only ask because in the last few years it seems to have become accepted dogma that veg has to be grown in a raised bed. Even on allotments people are being encouraged to build raised beds when what is meant is a DEEP BED.
There is a good argument to be made for growing in DEEP BEDS. This is where the soil is dug deeply with plenty of organic matter incorporated and then not trod on, the idea being to allow roots to penetrate deeply and easily thus allowing closer spacing between crops and hence more produce. These beds are usually no wider than 4 foot so that they can be reached from either side without the need to walk on them. It is not essential, but they are often edged with wooden boards to keep them tidy and I think that this is where people get confused with RAISED BEDS which are planting beds usually high enough to allow access without too much bending or from a wheelchair, or for ornamental purposes.
If you wish to edge a deep bed, I would recommend contacting a local timber merchant (a proper one, not a DIY store ) and asking for the price of some 1inch by 6inch treated gravel boards. Most merchants can cut them to length for you so they can be whatever size you require rather than what the manufacturers make. They should also be able to supply some stakes (2 inch x 2inch) for the corners and to support long sides. This invariably works out much better value than the ready made ones and is quite sufficient for veg growing.
Hope this makes sense and helps.