An Audi A3 or an A4 would be be a good car to mod, but not if the engine has 100,000 miles on it, it's not worth it.
I had a look on Auto Trader...the A3s don't look worth it but a couple of the A4s look alright. Personally I wouldn't buy a car or mod a car with such a high mileage, chances are they'll need parts changing on them fairly soon. Although, the only way to find out for sure is to check them out fully, and then test drive them. When dealing with high mileage cars though you can't expect a lot, they'll probably have a few scratches and marks on the paintwork and the interior definitely won't look new. The car will also feel like it has high mileage with it's handling (from my experience lower mileage cars feel smoother and more responsive). If it was me, I would save up a little bit more and buy a car (Audi or not... your choice) that hasn't got such a high mileage and comes with a decent (if not full) service history as most of the cars I've looked at don't even advertise service history.
Of course, depsite what anyone on this forum advises or thinks, it's your choice!
