The pen usually sold for queen marking is the Uni POSCA Marker Pen PC-5M.  The usual charge is £4.14 plus delivery unless you include this in an order of over £100.   Or you can by direct from Geoff Bazin for £3.50.

However the best value is S.E.T in Bridge Street, Haverfordwest who carry the full range of POSCA marker pens in all the colours and all the sizes – there the PC-5M will only cost you £2.99 and you will be supporting a local business.