I seek wisdom from you fine Travelziners!

Could anyone give me a good idea how much it would cost to rent a vehicle in London?......also, how much is petro?

How about Paris. How much would a rental be in Paris? Would I be able to drive to other countries with a rental from France?........how much more would it cost renting a car versus travelling by train (as well as local trains and the odd taxi)? Thank you.

Shawn Nunavut, Canada