Please, bear in mind that these sort of figures, whilst surely attainable, are built up over a number of years.
It's more reasonable to expect to make £200 per month as an average over your first year. If you go with that figure then anything else is a bonus.
The key to affiliate success is being able to suss what are the "converting" keywords as opposed to just gaining traffic willy nilly.
For example: If you knew that "link exchange software" was a converting keyword then you could bid on it at google and point the ad to a popular link exchange software product which pays over $120 in commission per purchase.
If you knew that 1/60 surfers convert you can work out how much you need to spend on ad's to make x amount.
This is traffic brokerage and it's just one way affiliates make money.
On the surface it appears to be "easy money" but in reality there is a lot of knowledge gained over several years being brought into play to make it work.