This is just a bit of humour, "cheap at half the price" is taking the mick, it means it's not that cheap at all. We use it all the time, I just heard my colleague hear of something that was expensive, and he said "cheap at half the price" meaning it was a rip off.

This is just a bit of humour, "cheap at half the price" is taking the mick, it means it's not that cheap at all. We use it all the time, I just heard my colleague hear of something that was expensive, and he said "cheap at half the price" meaning it was a rip-off.