Came across this post through the Engineering Council's Group page on LinkedIn and found it interesting. Good to see the IET being listed as one of the less expensive PEIs (well... mid range) to be a part of and also, for the IET to be mentioned by the OP elsewhere as one with the "broadest church". https://www.linkedin.com/pulse/comparethemarketceng-sean-moran/
I toyed with joining the IED (the least costly membership fee) before joining the IET and opted for the IET precisely because of its broadness and also because of its vastly higher level of activity.