Don't know a price in UK£... they're fairly cheap over here... lists at US$250 for a Micro-Can (which will do all A3's GTIOs Golfs, Jettas, GLIs, Passats, Tiguans etc) and there's a guy 100 miles north of here selling a used one for $150...
In the UK I think they're slightly more than the exchange rate might suggest, but they are WONDERFUL things.
Some people will suggest using Chinese knock-off interfaces, which are capable of running an older version of the software, but I'm against that for a few reasons.
But take a lookat the Ross-Tech site, and you'll see that they don't list that they just sell cables; they list them as "software licenses, including a cable"... Unlicensed knock-off copies are not eligible for support, and use of the software circumventing the proper cable doesn't do any good for Ross-Tech in the long run.
Ross Tech are a bonza company, who REGULARLY update the software -the last major revision was only last month- and so I'm all for supporting them.