Personal Trainers prices vary as PTs set their own rates. As a rough benchmark, outside of London, a PT session will typically cost between £30 - £65 for a 45-60 minute session; prices in London are usually higher at around £45 - £65 a session.
Factors that might influence the cost include their experience and expertise, location, and demographic, as well as the package - for example, if they offer WhatsApp support.
Some PTs may offer discounted rates for online coaching, or if multiple sessions are paid for in advance. Many offer a range of products and services to suit different budgets, so it's always best to speak to a Personal Trainer directly.