Pretty sure it's 19" not 18". A ton for a rock-solid, decent equipped, last-era steel framed Kona? Unless is hiding something nasty I don't think you can go wrong here:
https://www.gumtree.com/p/bicycles/kona ... 1158607702
https://www.gumtree.com/p/bicycles/kona ... 1158607702
