This is a recreational vehicle forum (motorhomes and camping trailers and such). I think you want a forum for home improvements.
Roofing prices for a regular stick and brick home can range all over the place depending on where you are located.
You location says United Kingdom so I have no ideas about roofing prices where you live. Here in the United States I am in Southern California and had my roof replaced last year. I have asphalt singles and to fully strip and replace the shingles on my 1400 sq ft (130 sqm) cost me around $16,000 USD) so to me the prices you are being quoted are way out of line.
Good luck on you roof.
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2001 Suburban 4x4. 6.0L, 4.10 3/4 ton **** 2005 Jayco Jay Flight 27BH **** 1986 Coleman Columbia Popup