There are lots of variables here, but my prices start from £76/month for group PT. Support and accountability are the biggest differences between having a personal trainer and just following a program.
Most people fail by themselves because:
a/ They don't know what they are doing.
b/ They don't hold themself accountable, e.g. Miss sessions, too many cheat meals.

c/ They lack support, e.g. If no one else seems to be on your side is easy to just give up. Often partners and friends don't want you to change for selfish reasons.

So if your missing one of those three PT is well worth the investment.

The base level for personal training in the UK is a Level 3 NVQ in personal training. The training commitment for this has reduced time and time again. It use to be 1 year of collage or 12 weeks as a condensed residential coarse. At time of writing this it was 6 weeks.
You want to look for someone who has continued to invest in their own education while gaining valuable experience with real time clients.

Riccardo, our coarse director, has over 30 years experience in an industry that most last 3 to 6 months. He also continues a program of self development and exploration.

To know if a trainer is right for you first look at their skill set and target audience, it's a bit like doctors, you would want brain surgery from you GP, would you?
Once you know they're qualified talk to them maybe have one to two sessions to see if you get on. Training, while not always enjoyable, should not be something you despise, or try to get out of cause you don't get on with your trainer.

Here at active NRG we are great believers in the fact strength is the foundation of all fitness. But that doesn't mean we train everyone like strongmen or power lifters. We meat you were you're at, that might mean working with just body weight exercise or less.

We aim to take functional body movement, like a squat, that we do many times a day and add a load to it. Allow recovery then repeat a little heavier.

Training frequency will vary depending on a number of things, like age, sex, other activity including work and other sport.
As a guide an average office worker in their 40s would achieve the best results from strength training 3 times a week, with increased low level aerobic activity every day (i.e. getting your steps in), and maybe a little HIIT work.
Were as an 60 year old may struggle to recover training 3 times a week, but may thrive on twice a week.