This is a difficult question to answer as there are so many factors to consider, such as the size of the door, the type of satchel required and the company you use. However, we can give you some indicative prices to give you an idea of how much you may need to spend.
For a small UPVC door, you could expect to pay around £30 for a basic security satchel. If you require a more comprehensive security system, such as those used on commercial premises, then you could be looking at spending upwards of £100.
It is always best to get several quotes from different companies before making a decision on which one to use, as prices can vary considerably. It is also worth checking whether any discounts are available, such as if you are buying multiple satchels or have a loyalty card with the company.