To be frank, there is no straightforward answer to this question because there are too many variables to take into account. you could try www.doubleglazingpriceguide.org.uk
Lean-to conservatories
spend the time to source for the best resources, you will be able to find a few good deals.
Before you purchase from any contractor, you may want to find out more about the products that they are offering at www.localconservatoryprices.co.uk/lean-conservatory
Cost of French Doors Fully Fitted
Make sure you deal with a FENSA; CERTASS accredited installer so that you have no issues with local building regulations. You can find lots of useful information here: www.french-patiodoors.co.uk/sliding-patio-doors
Aluminium or uPVC Conservatories
This will help you to choose the best aluminium conservatory supplier around your area.
Alternatively, you may want to try searching on www.lowcostconservatory.co.uk/lean-to-conservatories for more help.