Who has given you the price of £500, you should be albe to find a good re-map for less. We can offer you a re-map with the same power increase for £300 inc VAT (as an Audi Sport user). We are a Chipped UK dealer so the maps are top quality.
You will get an increase in MPG, most people see at least 10% but it really does depend on the roads you drive and how heavy your right foot is!
If you are interested in economy we can supply you with an ST3 multi map unit that will allow you to switch between a fast road map and an economy map when ever you want. You have to set it up your self and will need a PC with a USB port and email ot get it working. Alternatively you can come to us and we will set it up for you. These are £400 inc VAT for Audi Sport users and include the unit, leads, CDROM and 2 maps.