Just how low can you go? Forget a grand. Forget 750 quid. We’re testing six road bikes with a top price of £525. But we’ve still got very high hopes, as they come from Giant, Specialized and B’Twin, and from British out ts Boardman, Mekk, and Merlin. So, can you get a grand bike for half a grand of cash. And who will wear the entry-level gong?