Yes, cord and common thwn in plastic pipe is dandy. It doesn't have to be "flex" really, it's tuff and I got a spool of various colors, yellow, brown, green, black and white, red. I think I might have blue too, pull it from my building wire, one stock both jobs. I like 14 for most common lights, got nothing against a piece of cord to markers, enter the jbox with same connectors. Tying it in secure is what makes it last, enclosing the connections, no point in some exotic wire with a **** connection. Air brake tube for some, I have shoved it in all kinds of hoses but rolled plastic is great, it's super tuff, I got some wrecked extension cord I collected. For turn color the white as a yellow, use the black as a brown. Green right turn. I find some repair rewarding to find a good economical way of doing it,,, so much faster when it's cheaper and don't got to life save for every piece. There are enough parts you need without seeing how exotic you got to make it. Covering studs keeps from replacing fixtures due to rust. I bet speaker wire would work for modern markers. Common lamp cord. Very durable. Tie and tape up so it doesn't get pulled.
