We've had some mad as a box of frogs prices so far - 30-50k 
It's going to be 18 feet by 12 feet - no fancy features but a brick wall either end and a 90mm dwarf wall on the other walls, cheap upvc in white (wanted grey but there's no such thing as grey upvc, it's just white and then sprayed grey which I didn't know).
Lean to style, glass roof (pilkington one with uv)
Last time I had a conservatory done it was 9k for roughly the same cheap spec (bit smaller ) about 10 years ago.