Running costs are dependant on your ability, my running costs are at the cost of parts as I do all my own work, if it needs a garage then all dependant on the prices of said decent garage, saving a few pennies and buying a vcds lead and learning how to use it saves the price of having codes read whenever there may be an issue, probably pay for itself if you had to have the car diagnosed three times, can also change and code things so it's a very useful tool to have around.
Keep an eye on the air suspension, it's quite hardy unlike most systems but does fail, the compressor relay can stick open and burn the compressor out, there is a revised relay at audi for this and it's documented on the net, the rest is pretty much the same as most cars, it's quite common for crud to build up in the scuttle area and create water ingress into the car, also documented on tinternet, powered boot is also a little problematic as the hinges are prone to wearing and throwing the boot out of line, not sure when but revised hinges where made, not sure if by 2007 most stuff was ironed out.
One thing would be have the transmission fluid changed by a ZF a specialist, audi will tell you it's sealed for life but that's 7 years and 100k miles in their eyes, because they'd be quite happy to sell you a new car once the tranny blows up on your new to you car, there is also a documented issue with a hooting noise on hard acceleration which requires a fluid change and software update but again being a facelift I'm unsure whether this was already sorted out.
On a whole though they are a brilliant car and when I have to change this one I'm unsure how to better it, it'll probably end up being a FL 4.2tdi sport with map as its leaves above most things on the road including things like the 7 series and the s class.