Aerobic Step Advice??

Hi, I'm hoping that the wonderful members here will be able to provide some guidance. I used to like step aerobics, something fun I can do in the house with a DVD. Unfortunately it's been years since I've done it, and the step that we used to have has been put into the back of a storage unit which is now inaccessible!

So, my questions is where can I get a cheapish aerobic step that's sturdy enough to support my not inconsiderable weight. Argos has one for £15 that doesn't specify a weight limit, but it has mixed reviews. Any advice?