Whilst I don't do quite as many miles now I used to regularly do 30k per year. In the higher mileage brackets it comes down to depreciation on the car more than anything. I was working out Ford Mondeos costing me more than an Audi A6 because the residuals were so poor on them.
For a £500 per month budget for depreciation / interest on the loan I've been able to run an Audi A6 (bought at 2 years old for £19.5k loan and no deposit, kept for 3 years and ended up with £4k equity in the car) and an Audi A4 (bought for £26.5k with £4k equity and sold after 2 and a bit years with the same £3k equity left).
To make it work you have to hunt out the right deal and know what the car will likely be worth when you sell it. You also need to get finance cheap, both times I used personal loans at circa 3% and a £5k interest free loan my employer offers.
I would however agree with most of the above posts though, that if he can't scrape together a £1k deposit whilst driving his Exeo swapping to a 5 series or A6 sounds like a bad idea!