I'm a fan of Associated Press style, myself. If I recall, that means ¥17,000 would be fine, even ¥170,000, but you'd want to write out ¥17 million. If you write a script that automates this for the Web, share it far and wide. :)
¥17k (lowercase) works in a pinch (capital K means "carat"), but depending on the context I would consider a redesign to avoid confusion. (Also ¥17m for ¥17 million.) I've only seen abbreviated numbers used in print to provide a visual effect when labeling charts, for example.