I don't have any recommendations but I have to say good luck. We tried to do this and I couldn't find any contractors that wanted to get the permit for me. They all wanted me to hire a structural engineer to draw up plans first and then submit those plans to the county for a permit. We ended up building a short wall ourselves so we could avoid the permit process.
But if it helps at all, our estimate were 6K-10K for a 12ft 4 foot wall. Good luck!