Some people post some incredibly high labor rates on this site, but I would think $43/hour, especially on a 3 hour job is low for any landscaper anywhere. There is just too much to consider than time spent on the job. You spend time talking to customers before the work starts, loading up, picking up materials, wear and tear on equipment, book keeping, cleaning up. Plus the fact he called you because he could not, and probably would not be able to do this work. Most of these people expect to pay for your knowledge, equipment, and labor. Those that do not are best walked away from.
Many people who put up walls seem to charge by the square face foot. I break mine down into a price for the base and first row, and a price for what is added to that. As you know, there is an awful lot more time spent on the base and first row than the rest. I also consider the site. I charge more on a slope, areas with a lot of roots, etc.
$43/ hour would be good money if you work for someone else, but if you are the contractor, I think you should do quite a bit better than that.
Bryan Lafleur, misplaced cajun. Design/installation.