I visited a factory here in the UK last year (with some school students), who make plastic injection moulded parts and items. The CEO there said that yes they do manufacture a proportion of their goods in China but the reason that they still manufacture in the UK was that China was a long way away and in fact didn't turn out that much cheaper in the end so there was still money to be made by having a more responsive supply chain with more hands-on quality control. There is a lot of automation in injection moulding though.

I saw it quoted in three different blogspam articles, I basically googled and opened the first 10 results. I was having trouble finding a hard study - but people I know who work in manufacturing have quoted me "for us its cheaper to make it here" to "up to 20% more" so the 5% number didnt feel out of place.