Hike and Packraft – Drysuit options?

I've got a couple of trips planned with my new Alpacka in Scotland this winter and then a big trip in Iceland next summer.

The first mini trip basically involves a 100 mile hike over a few mountains to the source of a river then about an 80 mile decent to the sea.

Being winter and the fact its Scotland.. I am fully expecting horrible weather, big water and cold condition and currently have not managed to find a suitable solution to staying dry and warm (ish) on the river section while not having to carry a heavy dry suit for the 100 miles before.

Does anybody have any thoughts on my options or know any cheap drysuit manufacturers who produce lightweight dry suits that would fit the bill. I blown all my money on the packraft so its got to be as cheap as possible!

Any help would be much appreciated.

Thanks!