Because of its popularity there is quite a bit of competition. The leaders around here are creative edge it's a really nice seamless dual layer curve looks especially nice when it's edged with a blade Edger last I sub contracted out to them it was $10 a foot
Cheaper options are just square concrete poured in looks nice but the quality isn't the same between 1-5$ a foot
I generally install brick edging or black plastic both work nice but requires more maintenance