A rack is not hard to make with a sawzall, a drill and some bolts, and of course your choice of material.
But since the material world went crazy a couple years ago I'm not sure what you might find.
One I added onto an aluminum camper topper with just 4 side legs sticking up above the camper top and two cross members to carry the material. We were nearing completion of a project and I was hauling off anything worth having that they didn't want, and one load was a bunch of 10 -12 ft 2X12's that made a pretty hefty load.
BTW, this topper was on a 1980 Chevy LUV pickup, and that load of 2x12's had me going all over the road and barely making it around some corners, but that rack held it together all the way home
I made that one with small angle iron from a rack at an Ace Hardware Store, even then the prices weren't so rediculous
Another was on a 87 Ranger and I built it with a jobsite portable band saw and some structural bracing they were done with. I still have a few pieces of that in the back.
It isn't hard to come up with a rack and if you are any kind of a handyman at all, actually I am a commercial carpenter, but still it doesn't take that many skills to make a decent rack out of almost anything.
Trim it up and paint it and nobody ever need know it was an old bed frame or left over roof bracing from a warehouse and showroom roofing system
Picture it, cut it, drill it, bolt it, paint it, Load it!