'Composite' as it is used in the world of boating ads often refers to a hull where the glass cloth has been replaced by a high tech material like carbon or kevlar. Do be aware that the builders were looking for lightweight and the boat might have a shorter life.
However I have also seen it used to describe a boat built using wood with epoxy
see here for more info. WEST SYSTEM | Projects | Profiled Boats - Wood/epoxy longevity
While I would not dismiss a boat built with either method the vast majority of boats you will look at will be good old GRP but there is a hidden problem with many older boats that were built with wood cored decks. The wood rots if water is allowed in. Many threads on this. Try to find one with this problem and walk on the deck so you know what to 'feel ' for.
Lots of boats around in that price bracket, look hard and you will find something that has all the kit and no major problems.