You didn’t do this with plants. Pea gravel isn’t going to fix this. $15k is too much for pea gravel combined with actually fixing it. Call a mason. Not a landscaper. I’m not disparaging landscapers, I am one too, but I’m also a trained mason that dips his toes in retaining walls and patios. A rectangle (mason) is a square (landscaper), but a square isn’t a rectangle. That said, I wouldn’t hire a mason to grade a driveway, excavate a foundation, plant trees, or to install sod. Just because on paper those shapes have an odd definition, they are not the same.