Conservatory prices depend to a large extend on how much it is a fashion to have one. This makes that you can find constructions called “greenhouses” in quite the same quality for a lot less. If you don´t need another fully heated living room, but mainly a somewhat sheltered extension of the garden, its worth thinking about it.
Naturally a lot depends on size, shape, materials. So usually a specific price is only possible to calculate after some planning. Considering that it is too often even quite difficult to get a PRICE RANGE from a producer. So here are some numbers:
A medium sized (30sqm / 30 sqf) cedar wood conservatory kit from a classic British manufacturer like Amdega or Marston & Langinger will cost quite as much as a medium sized car - appr. 30,000 Pounds / Dollars / Euros. Calculate another 10,000 for building work and another 10,000 for fittings like tiling and underfloor heating. Now both companies don´t really make cheap conservatories. In terms of design they set a standard.
If you know how to swing a hammer and are willing to compromise when it comes to customization, there are some quite cheap DIY conservatories on the market.