8ft concrete posts are around £15-20 each, 6ft long 300mm gravel boards are around £10-15, 5ft*6ft fence panels go from around £10 for a cheapy to £25 for an expensive one, bags of cement £2.50 each, bags of all in one ballast £2.00 each - premixed post concrete around £4 a bag.
Remember you need to bury the post at least 600mm (2ft) in the ground so you need to match panel and gravel board size to post lengths - i.e. 5ft panel + 300m gravel board + 600mm in ground = 8ft post
In the better quality posts the panel groove stops about 450mm short at the bottom end, meaning where the most stress is its solid. They are also generally a smother face so higher resistance to frost attack
As for building it, line and level your first post concrete it in with a very dry mix (moisture in the ground this time of year will be enough for the mix), drop in the gravel board and set your next post with it on place then you know it fits and don't look a dick when you cant get the panels and boards in later because its moved
Tip tip:- If you are replacing an old fence, make the first panel of your new fence 3ft wide (or a different width to the old fence) instead of the same width then, when you dig the holes for your new posts its not on top of the old ones and you don't have to dig all the old concrete out
