Lol, our first two dogs cost exactly that, 50p, from 'ponty' pontypridd market lol.
First one, about 1969, six weeks old, 'rusty' as he was a rusty brown colour lol, aggressive beyond belief, couldn't stroke him or even put your feet on the floor, or he'd be savaging you!! He went back to the market after 4 days lol.
Second one, about 1970, 'snowy' as he was all white, with just a small patch of very pale fawn/cream on the right hand side of his head. Apparently, his father was a show type whippet, mother just a small mongrel.
He was a lovely dog, but 'went missing', stolen