Had my audi A3 diagnosed with the same problem. ESP light became permanently illuminated on dash. Thought nothing of it but nearly passed out when they did the diagnostic on it and said the ABS pump needed replacing at a cost in excess of �1000. The fault code was 'brake pressure sender 1 - g201'. Went home and started researching that fault code. Turns out the pump fitted in A3's 2004-2008 is prone to failing. It's the same pump fitted in VW Golfs, VW Tourans, SEAT Alteas, SEAT Toledos, SEAT Leons, Skoda Octavias, BMW 1 Series, BMW 3 Series,
Volvo S30s, Volvo V50s, Mazda 3s and Mazda 5s. Many effected customers have had 'goodwill' offers to help cover the cost of the repair either partially or in full. How much you get back depends on vehicle age, mileage, where purchased and serviced and any other variable they can make up as a potential get out clause.
Armed with this info i approached my local Audi dealership who point blank claimed they had never heard of this problem. However a week later i was offered 50% goodwill for this supposed uncommon problem. I've refused this and and am in the process of battling it out with Audi UK. I don't see why i should have to pay anything towards their mistake of fitting A3's with sub-standard parts. Incidentally Audi UK are also claiming they have never heard of this fault. Be under no illusion this thing is huge. Check out some of these links to get a feel for what is going on and don't let Audi muck you around - which they will. Incidentally my car is only 4 years old, 50,000 miles on the clock and bought and serviced within the Audi group.
Honest John: VAG pays towards VW Touran ABS control unit faults - Telegraph
VW pushing me to braking point - Telegraph
Auction Values of BMW 1 Series Set To Drop | Motoring News | Honest John
Audi A3 ABS Pump Module - ECU Testing
Volkswagen Golf V (2004 - 2008) - 05 1.6 ESP Light On Continuously | Technical matters | Back Room Forum | Honest John
Honest Johns take on ESP problems - BRISKODA.net - Page 3 - The Skoda Forum and Community
This is just a snapshot of some of the stuff on the web. There is also a facebook page for VW Golf MK5's with the ESP fault- worth joining aswell. It's the same component just different car. Good luck getting it sorted.