You might want to try Formatt filters. Not widely advertised in UK although they are made here they sell in the US as Hitech. Most reviews put them as better than Cokin but not quite as good as Lee. They do both professional (100mm) and P Mount (85mm). In a P Mount their ND @ density 3 (approx 9 stops) is £21.28+VAT and postage so probably around £30 all in.
http://www.formatt.co.uk/stills-filt...d-filters.aspx