One of the simplest ways I know of is to use metal t-posts at each end of a row, for rows longer than 10' maybe include some in the row as well. Then take 18"-24" 1x1 blocks or other similarly sized pieces of metal or wood and fix them to the t-posts at ~24" and 48" off the ground. Then run one wire between the ends of the cross pieces down the length of the row to create a suspended wire "box" that will support the raspberry bushes as they grow. t-posts and wire are pretty cheap and you can probably find them used if you look on craigslist.

Galen

Here is a link that might be useful: Edible Garden Northwest