Single, 10' length of FRP, 1/4" wall, 2" square section is just under $100 at McMaster carr. 1/8" wall is also listed. PVC, wood, is all very second rate.
Exactly right, thick wall square section fiberglass is very robust. It looks really good and is not going to get that very sad, saggy look like PVC does after one summer or auto-magically shatter into a million pieces on a windy very cold winter night.
PVC is definitely not rated for structural-anything. The fiberglass military mast kits would be a much better choice and come in 4' lengths if you were going to go that route. At least you could use the rest of them for a 20-30' tall field day antenna