I agree. If the slope is eroding then it is best to address firstly at the point where there is any directed waters. Diversion at the top of slope is key.
Secondly, address the slope itself to protects from direct rainfall. Textile/stabilization works well on slopes to a certain degree. Depending on grade of angle. Myself, do not install on a slope any steeper than a 2:1.
Problem with textile material, at least in my experience, is that they are black. This has proven to be an issue as the material gets so hot while in the stages of trying to grow vegetation that the heat kills off the vegetation.
Cement soil stabilization also works well. There are also polymer products that work well but availability here is unknown.
Depending on slope size and availability of stone in your immediate area, it may simply be best to hard armor, install large stone on the slope. I say this as labor is far less expensive than paying an engineer and buying costly materials or services.
Many years ago I seen a slope stabilization product installed in Pattaya that I had never seen in my country. It was a textile material, accordian type, 3" deep pockets, that was pinned to the slope then filled with material, small stone or grass. I found the product in my country and utilized it on a project with excellent results.
I was just in Pattaya, passed by the area and the slope is still in tact. Whether or not the slope has been reworked I could not say.
And yes, I would agree that a soil stabilization expert here may be expensive.