If your looking for a particular vechicle go here and select vechicle enquiry
https://www.taxdisc.direct.gov.uk/EvlPortalApp/app/home/intro?skin=directgov
put the number plate in and the make and it will tell you the road tax and when it's due on a vechicle.
As for 3.0 TDI's I know this is a B7 forum but recently I have bought an 08 plate manual B8 A4 3.0 TDI Avant.
My previous car was a B5.5 Passat 1.9 estate mapped to 207bhp so was looking for a silmilar size car with similar performance.
I was looking for quite a while before I came across this one. I wanted a B8 as Audi made quite a few improvements over the B7.
Garret 2260VK turbo is a good deal better than the BV50 fitted to previous engines, This contributes to more power and better mpg.
The B8 is about 10% lighter than the B7 due to a lot of things being made of aluminium and body panels from high strength steel.
Despite the fact that the car is bigger than a B7.
The B8 3.0 TDI uses a twin plate 228mm clutch, so shouldn't have any issues with remaps unless you go silly.
Changes to the way the FWD is passed to the front wheels mean that the wheelbase is extended along with the change in torque split from a 50/50 to 60/40 makes the car a better driver and less likely to suffer from understeer.
The early B8 cars like mine came with the CAPA engine which is EU4 plus and CO2 is 188g/km so road tax is £260 a year, I have seen cars only a few months younger than mine on 08 plates with the CAWA engine in which is EU5 and has a CO2 rating of around 178g/km this is £220.
If you can stretch to a B8 I think they are a better choice but I found that manual cars are pretty thin on the ground. I bought mine private off autotrader. I have seen them for just over 10K but they usually have 120K miles on them.
Mine returns around 33-34mpg over a tank but I do lots of town driving the average speed on the trip is only 22mph. On a run it's easily into the mid 40's.
Karl.