Yeah because a £15k S2000 is going to be worth less than £4000 in 18 months... seriously, stop posting drivel.
If you are only getting a loan for 50% of the value of the car then the car is never ever going to be worth less than the remaining amount on the loan. You won't be in negative equity with the car so it's a relatively safe purchase imo.
If you can comfortably afford the repayments then why not? it's only money and you only live once. You could get an older S2000 for less though.
It's hardly drivel ..(seriously!11!).
An unsecured loan of £7500 across 3 years at 7.70%APR works out at £8350 or thereabouts, total repayment.
The car costs 15K, for a nice 2004, which in 3 years (crudely calculated based on existing prices, not factoring in increase in fuel prices/tax and the effects they will have on the second hand car market blah blah) will be worth around £9000, that's a drop of £6000.
So his initial purchase costs £15,850 over 3 years, (£8350 in finance and £7500 cash, not including running costs) and he is left with a car that's worth £9000. Meaning that in 3 years of ownership the OP loses £6850 (again not including maintenance). The S2000 is a lovely car, but I wouldn't want to lose above 7 grand on a 4 year old honda over 3 years.
In the meantime the OP could bank his £7.5k cash, save the £7k he would have lost in depreciation/finance APR, and put aside his £250 a month and buy something outright in 3 years. Not having to worry about a change in financial circumstances etc. Finance is great, but it's also the worst thing ever.
*Disclaimer: Any one of those calculations could be completely wrong.
