Updating bathroom with a walk-in shower unit.

The prices are indeed eyewatering! I was quoted over £8,000 to have bath removed and replaced with a walk in shower with screens etc.
That was from one of those firms you mention.

I got a local small business to do the same for just over £3,000. He did a fantastic job which also included co ordinating wall panels, grab rails etc. I have since put 3 people on to him and they are all equally pleased.

They are expensive, but if you can afford a walk in shower do get one. I love mine. Ensure it has what you need, grab rails and seat if needed , non slip surface , mine is officially nonslip but I always use a long suction shower mat just to be sure.
Some years ago now so unable to give you approximate cost. There is such a wide choice, have you a family member or friend who can help you with your choice? Good luck , if you go ahead I don't think you will regret that decision.