Don't know how professional you need them to be but Vistaprint do 250 cards for free (just pay the postage) but you have to use one of their selection of designs. http://www.vistaprint.co.uk/
You can upload your own design.
I paid £20 for about 1000 cards
@pastry_lover started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
You can upload your own design.
I paid £20 for about 1000 cards