A good archery shop ( Aardvarks) may be able to fine tune the draw length via a different string. I reckon worst case, it will need new cams and a string, budget for anything between £35 (new string) and £100 if it needs cams as well. If you get the bow at a good price it may be worth it. Used bows usually need a re-string anyway, just to make sure they are safe.