If you have a compressor, Bunnings is your friend.
$20 spray gun, Walpamur fence paint (water based, quite a few colours available), 100 ml of water mixed into the gun pot with the paint to thin it down, and spray away.
It took me no time at all to paint all my fences and easy to clean the gun in water (or chuck it if you you can't be bothered cleaning)
Cheers Johno