To be honest, I my flying profile was the same. During PPL training, I racked up the hours...but on getting my PPL I just didn't fly as much, and it wasn't due to cost.
I also think, that using cost as an excuse is just that...its an excuse. Flying should become cheaper after completing your PPL because you can solo-hire the aircraft as opposed to having to hire the instructor as well. So what's the real reason that you've suddenly lost interest in flying.
For me, it was because there wasn't real excitement in it anymore. As a student, all the planning decisions are made for you. There's a course structure that you follow, and the instructor will tell you where to fly to, &c. As soon as you've got that PPL you've lost that structure and guidance.
The solution is to set goals and challenges for yourself, and to prepare a structured development route to get there. You might want to start to experiment with touring, and flying to an airfield that you've never been to. It might be a quiet and boring aerodrome, or it could have an exciting and vibrant atmosphere with lots of interesting things to look at. Until you've been there, you'll never know, right?
The other option is to fly more exciting aircraft. Have you thought about a tailwheel conversion course, or a seaplane rating? You might not continue to fly these types of aircraft but it'll be a fun experience. I wouldn't recommend buying your own aircraft or even entering into a group/share until you've explored a bit and decided what sort of flying you want to do.