if you find a decent general bike shop (not a roadie's paradise or a mtb specialist) you can make some bsos usable for a few quid. my wife's awful apollo premonition was, for £40, turned into a perfectly ridable, if heavy machine with the addition of some second-hand solid forks, some £7 a pair set of brake calipers (unbranded, but still good entry level) and new cables (fitted).
admittedly, that bike did at least have shimano megarange gears and brake levers/shifters, so it probably wasn't as poor a bike as the ones you can get for less than a ton from a supermarket.