The way I think is this how much are you going to spend on your waders, dry trousers ect compared with the cost of a dry suit that we all know does the job better and in a capsize in winter could save your life.
Most if not all of dry trousers and tops are more suited to sit inside kayaks with a spray deck/skirt, but for us we have to take all of the weather like it or not.
As for dry trousers this is what I do using a wetsuit and boots with no zip, put on the wetsuit trousers and tuck the boots inside, make up a Velcro strap and put is round your ankle make sure it is really tight to make a good seal, once launched release the strap you will have no wet feet and will keep you warm,I use this set-up when the water temperature is not too cold
I know it is a big out lay buying a drysuit, but well worth it in the long run.