First time buyer requires ££ advice

[jasonsensation]

I'm looking for some advice! I have the opportunity to get a Black Ceramic GMT on Interest Free Finance over 2 years, with only a 10% Deposit. Now another ''up'', is also the fact the Authorised Dealer is not keeping the warranty/papers etc.
My overall Goal is to own the much sought after GMT Batman, however it would mean placing a deposit with a different store, and i would need to take out a Personal loan resulting in paying back huge amounts of interest. At what point is it better to buy the black ceramic now, and be content with that instead of getting the Batman and probably end up paying back £1,500 in Interest over 5 years.