But ask around friends and neighbours for your local independent plastic-door-and-window-and-patio-doors repairperson 9there will certainly be one)
I've had double-glazed units in windows replaced for an average of around £50. A large door, reglazed in laminated glass (for burglar resistance) was a few hundred.
For the person who knows how to do it, it's a trivially easy job. If I'd known beforehand how cheap it was, I wouldn't javer put up with misty windows.
You can have them changed to obscure glass, or matching glass, or security glass if you want. The sealed units are made up in a factory, to order, so there may be a delay of a week or so between measuring up and fitting.
These people can also adjust or repair hinges, locks and latches if necessary.
I found mine through the window cleaner.
Don't go for a big brand company, but do get a personal recommendation (websites where traders pay to be rated or trusted are not recommendation sites, they are advertising sites)