I've just been quoted 900 to replace a bonnet with new, repaint and blend into wings, etc. I'm not sure what the cost difference would be between the two but the labour has got to be similar, as this is mainly in the paint and preparation, unless anything major needs straightening out.
I'd agree with TB. either the repairer is bumping the price up as it's an insurance job or the damage is more extensive than it looks. Worth getting a second opinion pointing out that you were quoted 2.5k and it's a write off (so if they don't quote competitively, they won't get the business).
Have you got a copy of the repair quote? These are normally generated by an industry standard piece of software and are itemised to show exactly what they've quoted for.
Have a look and see if they've bulked out the quote by charging unreasonable amounts under "paint", "workshop materials", "charges", etc.
To give you some idea mine broke down into 237 quid for a bonnet, 374 labour 144 for paint and materials and 13 "charges"
If there are a few bits of trim, headlights, etc in that bill I can see it getting quite large and you could bring it down significantly by sourcing parts from a breaker.
Kevin