They make a very inexpensive edges made of vinyl or rubber . It is flexible , it comes in a roll , you should be able to get it at home depot , Lowe's or walmart .
The black plastic edging will work good and last a very long time. I am replacing mine this year, it was put down in 2000 and only a couple of cracks. I lucked up and had someone give away quite a good bit of brick scalloped edging on facebook a while back and that's the only reason I am taking mine up now.
Here are some good ideas (the terra cotta pot idea is brilliant!) : https://homesthetics.net/17-simple-cheap-garden-edging-ideas-garden/
Here are some options! Good luck :)
Wal-Mart sells rolls of edging for $10.00 for 30 feet🐕