It is relatively simple to find a few websites that offer high-quality and cheap composite doors and in most cases, you should take the time to check out at this comparison website first https://www.doubleglazingpriceguide.org.uk/ which is all about getting good prices
This is highly recommended because they have articles & sections on many different types of doors, such as:
There are some companies that manufacture inferior doors, and they sometimes sell them off at high prices so consumers may be misled to think that they are paying for something of good quality because the price is high. I would urge you to look around on the comparison website www.upvcpatiodoorsuk.co.uk, so that you will be able to identify those companies that you can trust.
There are also a few companies that offer free quotation, so I think it is good if you can engage them to give you a quote. This will also help you to decide on the amount of money that you need to spend.