dirtyharry said...
.. won't get boring too quick, but at the same time something I could put around in the river with the kids on and get the missus to have a crack at
That's a big requirement. The 170 size will do the job for the wife, kids and the river. .. but I bet you that once you get a taste for planing, you'll want to progress to the 90-110 size and sail the ocean or the lakes. Given your kiting/surfing background, you'll take up windsurfing quickly.
The beginner boards are expensive and rare. Not a lot of demand for them. You can scan the Buy/Sell section for months and not see anything (I did this once). I'll PM you some places that might have some 2nd hand beginner gear.
Welcome to the sport