Ultimately you need to ask yourself whether you want cheap motoring, or a new car?
If the former, then fixing the existing car is the obvious solution. Yes it's £1.5k, but if your budget is £8k, then that still leaves you with £6.5k for future repairs which may or may not be needed.
If the latter, then fine, but that's of course going to cost you, and there's no guarantee that any car you buy for £8k is going to be problem free. Yes you get 6 months of consumer protection (assuming you buy from a dealer), but:
A) There's a significant difference between those consumer rights existing, and actually being able to fall back on them without some sort of battle
B) After those 6 months you're basically on your own and if the new car throws up a £1.5k bill after that, what are you going to do then?
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If you're looking at an EV for the new car, then as far as fuel savings go:
- We'll assume the current car does 45mpg (taken from here), at current fuel price of £1.56/l that's ~15.75p/mile
- We'll assume any EV you buy gets ~3.6 miles/kw and that you charge exclusively on a cheap tariff, e.g. Octopus Go at 6.9p/kw, that's ~1.92p/mile
- 15.75-1.92 gives a difference of 14.46p/mile
- For your 10k/year miles, that's a total of ~£1446 saved in fuel - we'll round that up to £1.5k to make the calculations easier
- Subtract ~£1k from the first year to have a charger fitted
- Subtract £1.5k from your £8k budget (for the repair which wouldn't be needed), leaves us with a value of £6.5k to break even.
- £6.5k - £500 remaining from year 1 gives £6k
- In 2027 you'll save £1.5k, leaving £4.5k
- From 2028 onwards you'll save £1k (due to the 3p/mile tax on EVs being implemented), so that leaves a further 4.5 years, giving a total of 6.5 years to break even
So yes, if you're happy keeping the "new" car for 6.5 years then it could be the sensible option, but that comes with a whole load of assumptions, e.g. no repairs for either vehicle, fuel prices stay the same as they are currently, etc.