Welcome to RB, Dilly.
The Sunn Notion was never common in this country, so not many people will know what it was like or a value now. It's a bit out of my experience too, so posting a picture would help a lot. I'm guessing it's a sandy colour one? It was lowish in the range, budget steel tubeset, designed for short (60mm?) travel fork, but will work fine with a longer (80mm) without upsetting the handing much.
At the top of this forum is the "one and only how much is my bike worth" thread - might be worth asking there.
For used forks , trawl the classifieds here or search e-bay.
Good luck!
And here's a link to RetroSunn http://www.le-jurassien.com/sunn/catalo ... mmes91.php
Thanks for that. Its chrome in colour with only added bits being an orange mudguard at rear and another orange plastic guard on lower bar (below bottle holder).
i paid i don't know £80 for a broken tonic frame only (same frame as this, but with green bubbles, i kind of like green) orange never were my thing, but if green, well £200 plus pp.. but then i lack sence of moneys value