I had an implant about 20 years ago that went wrong. I had an infection under it. I then paid for an operation in an attempt to deal with that, although the surgeon explained that it may not be successful. It wasn't, and then I paid to have it removed, I now have a gap there.
The £27.000 I quoted above was, I suspect, in part the cost of treatment in a such a very smart establishment. State of the art etc. It included 4 implants, bone augmentation in places etc. I had already paid for scans.
I got a second opinion with another dentist, but for far less work than the original. That was for £5,000. Even so, when I read the process and the length of time it would take, I began to doubt my courage for dealing with such a procedure. But I am a notorious wimp. I just am. I chose not to go ahead with that either.
I'd say do all the research and get more than one quote. I do think implants are an excellent solution to keeping a good set of teeth, and also for retaining the shape of your face.