Just as an idea, if it doesn't have to be 'new', have you considered a 15 plate used car?
A quick look on the Mercedes used car section suggests they've got dozens of C250 AMG Sports versions, loaded with kit, 15 plate all with 6,000 miles on the clock and all at around £26,000 / £27,000 if you bought them without any haggling.
They'll still do PCP deals on them and still have low interest.
You save about £6,000 for having a car that's 6 months old.
the one above is 220 CDI AMG Sport edition, diesel, auto, tiptronic and every extra known to man - 5,000 miles - £24,450 on the windscreen.