Beach Art Additions

While the weather takes its toll on the various beach art installations, from time to time there are quirky additions to the assemblages. There currently seems to be a small figure atop the Joppa Tardis and a washed up welly next to it - reportedly half of a pair that costs over £100 new. If a pair costs £109, what is one boot worth? Next to nothing, presumably. And yet combined with another near worthless boot to make a pair does the value shoot up?