This is a tricky one. Tbh, like a lot of people have mentioned already in this topic it depends what you are good at. If you know a thing or two about mountain bikes or mx bikes for example, if you seen a not so great bike but had good parts on you could buy the bike, strip it down and wait till a beautiful frame comes along and put all the gear onto it. In a sense you win win because you can then put all the old things of the frame and put them on the cheap bike. Then you sell the good bike you've done up and you've got a bike for yourself. Loads of ways of making money, even download virtual dj buy some music and do some mixes. Once you experienced do a mix and wack it up for 15/20 quid 5 sales you've got 100 pound off maybe 10 pounds. What it is with the internet is time and patience.