We don't have lawn and the adjacent landscaping areas are barked. We mainly need to keep the gravel in the walk; keeping the plants out is less of an issue.

I'm wondering if there are affordable composite materials in a 1x4 to 1x6 size that could be used and that would be compatible enough in appearance that we wouldn't have to replace all the edging at once (total path length is >200 ft). We need something stiff enough to stand some side pressure, as sometimes the walk is raised or sunk compared to the landscaping. The plastic stuff that comes in rolls is too light and won't meet that need. Yet we have to be able to bend it as the path curves.

I'd appreciate any suggestions on materials.

It would be a one-time expenditure of effort -- much like replacing the edging. Then it would just be a matter of adding a bit more bark than you would when you refresh the mulch around the plants.

With some luck, a Craigslist ad might locate someone happy to haul away the gravel.

Disclaimer: yes, I'm not fond of gravel. ;-) Or of the round white rocks I inherited from the previous owners.