There is no standard price for managed cyber security services in the UK. And there shouldn't be.
The cost depends on what you're protecting, how complex your environment is, the level of monitoring and response you need, and how much responsibility you want the provider to take.
A service that monitors 500 endpoints during business hours is fundamentally different from a 24/7 managed detection and response service covering a hybrid environment across thousands of assets.
That makes headline price comparisons difficult. More importantly, they can be misleading.
To understand what you should expect to pay, you first need to understand how cyber security managed services pricing works, what drives the cost and exactly what you're getting for your money.