A. The mini implants that you are talking about is a very straight forward procedure. You can expect to pay approx £600 per mini implant. You will probably need at LEAST one on either side- possibly 4 in total. Then there is always the charge of relining your existing denture. Many people opt to have a new one made from scratch, but this all depends on your own thoughts.
Not all people are suitable for mini implants and everything depends on the quality and level of bone you have. I would discuss the options with your dentist.