My wife and I have been fostering for about two years now. First as respite carers, now with a full time placement.
We went to the local authority, in our case Aberdeenshire. It involved quite an extended training process leading to a panel interview before final acceptance – took about 18 months all together. Not sure how this may compare with other agencies.
There is a scale of recommended payments to foster carers, which I think most local authorities will conform with. I have heard, anecdotally, that some charities pay higher rates but on the other hand you may be dealing with more difficult children. Not that most people are in it for the money.
Good place for more information could be ‘The Fostering Network’ – http://www.fostering.net There is a massive demand for new carers. All the best if you decide to go for it.