The backpack is back. Designers from Chanel to Valentino have embraced the hands-free bag. But those designer backpacks often have a hefty price tag. So what to do when you, for example, love this Stella McCartney backpack (£755/€835/$1,295) but dislike it’s price? You simply have to find a high street alternative like this Forever 21 (£25/€28/$32.90) version. What to do? Splurge or save?