I have what sounds like a very similar conservatory, had a few quotes in the last month.
For replacement of everything above the dwarf wall with white PVC and a polycarbonate lean too roof is about 10k (11k with a double door).
For timber effect PVC, with a solid Edwardian style roof was 20k including build regs and door etc.
This is in the Bristol area for reference.
Ultimately, decided we’d prefer the latter, both as the current room gets far too hot, and a solid roof would both enable the use of the room alot more and it would value to the house, moreso than replacing relatively like for like.
Now, saving up for that is going to take a fair while so just hoping the current conservatory doesn’t fall down in the meantime!