After Hours

Hi guys, im after some advice. Ive recently built a man cave at the bottom of my garden and im after extending my virgin tv down to said cave. Ive been advised best way to do this with out getting a third reciever box on the property is to get a HDMI cable, id need one at about 50metres long. Whats the cheapest way of getting one as id like to have a go at making my own but im unsure of what cable to buy etc, thanks for reading my long winded waffle :-)
Jim