Last summer I bought some poles from a sawmill, they come in 12' lengths and I paid about £3 each for them. You can buy them 3" or 4" dia and I actually bought the 3" diameter ones as they are lighter so carry around and so better for use at home.
They were already weathered and I coated them in undercoat then gloss, I had great fun painting the stripes on!
I would definitely recommend doing that as it is far cheaper and you can choose your colours!
This summer I intend to have a go at making planks.