Cheap ones on Ebay won't work
Think there are some leads now available which will talk to the CANBUS system but they're around £50+

In all honesty if you're keeping the car long term then I'd advise getting a genuine lead. You'll not only save yourself money on diagnostic fees but you can pimp out your services to other members, friends, family etc and recoup your money

I've done this and paid for the lead well within 18 months or so