Walls – Inexpensive ideas to extend the height of the fence cinderblock wall outdoors

I live in the desert and a local bud of mine used landscape grade timbers that he attached vertically onto the cinderblock wall every 8ft. Then he laid outdoor rated privacy fabric over the timbers and stapled them along the wood timbers. And apparently, the fabric isn't drooping between these the studs as they is no horizontal structure supporting the fabric between the studs he placed every 8ft. So now his privacy went from being only 6ft tall to being 8ft tall. I'd like to do something similar but when I was at Home Depot I discovered that the 2'x4'x96" rated landscape timbers were over $10. I have approximately 300ft of length I want to cover so at that price it's going to get costly. Especially when you consider the cost of regular 8ft long 2×4's for interior use are about a fourth of the price.

Since I live in the desert and we only get on average 4-5" of rain per year can I get away with using interior wood and painting it with exterior grade paint to seal it? It does get hot here in the summer (can get to 121 degrees in summer) so not sure if I would have to worry about warping due to extreme heat. But since the timbers are going to be attached with tapcon like screws along a six foot tall wall only 2ft will be up above and unsupported and that would be the only area that could warp.

Would my idea of painting the wood to seal it work or are they more affordable suggestions?

By the way, here are two photos of his project. The first one was before and the second is after.

In my case, adding two feet of additional height will block all of my neighbors windows from looking right into mine.