Any printer around that price is a false economy. The ink cartridges will be minuscule and cost a fortune to replace. If you look at another thread about printers you'll see the calculation I did which suggests that an Epson 3880 at £900 is actually a cheaper *printer* than some other consumer model which costs about £250, when you factor in the included ink costs. So cheap printers aren't cheap, basically.
The other point is - if you expect people to buy your prints, surely you should ensure that the product is of a reasonably decent standard in the first place, which a £100 printer almost certainly won't give you. If you buy new. I did kick off my printing career with an Epson R2400 from eBay which was decent enough for a bit. But in reality you'll need to buy a Canon Pro 100 if you're going to be doing prints which you want to sell. That's going to cost a bit more than £100 unfortunately.