In modern buildings constructed to meet present day building standards some form of ventilation is also necessary & Trickle ventilation will satisfy that need. To find out more about modern replacement windows, check out this page: mylocalprices.co.uk/cost-guide/double-glazing-prices
It’s just very difficult to give an accurate price for a “supply & fit” job without visiting the site of the work and carrying out a survey. The best thing you can do is get several quotes and compare them to see who’s offering the best deal. Go here for Double Glazing Cost 2020 – Latest Windows Prices
Do the right thing and live in peace with a modern double glazing in your doors & windows. Find specialist doors here: UPVC Stable Doors | Composite Stable Doors Prices, Designs & Features