You don't typically pay for a PhD. You're accepted into a program and the schools pays for you, sometimes even with a stipend to help with living costs
The UK has a highly competitive system for a limited pool of public funds, many students are self-funded in PhD programs. The UK has some great programs but unlike the US and continental Europe it is highly skewed towards the upper classes as the only requirements for entry are basic competence and money for the fees.
It depends on the subject. Amongst mathematics PhD students, at least, it seems that almost no one is self funded. But you're doing history or literature or something, that's another matter.
