£10 is the regular club membership with (at some point in time) gets you a club pack and access to show your car at PNG attended shows/stands etc. Some discouns on bits too but they arent vast.
the 6month and 12 month ones are for traders, eg one man band all the way to proper company selling wares on here need to be traders otherwise its taking the piss.
for reference, I dont think you "need" to pay membership to have a project thread, unelss you want to hide it in the club area of the forum to stop the general pubelick from seeing it. Not trying to disuade you, but giving clear honest options so I dont get flack from others