It's not really about paying money into the system, it's to do with how much they've worked from what I can gather. For example, no matter how much money Man City offer to pay someone from say Brazil, if they haven't played a certain number of games at International level then the government department, I think it's the Home Office, wouldn't give a work permit. Occasionally there is certain circumstances that allow them to bypass this, but it's all very technical.
Although with Guzan I think he might be ok to get a new permit as he's played enough games at club level.
Ok I think i've confused myself now & can't get back onto my original thought but i'm sure that there's someone on here who can put it in simple terms.