It probably depends a lot where you live. I'm not in a posh town so there certainly wasn't anyone who could afford a private birth!
In my group there were six couples, the mums all aged 26-34, variety of occupations from doctor to supermarket assistant. Four married, two not. Three BF, two FF, one mixed fed. Two wealthy, four skint! Three BLW, three puree weaning. None co-slept apart from as a last resort when bubs wouldn't settle! All went back to work, one full time, five part time. No cloth nappies and lots of processed food! But really, all that is irrelevant. You might meet a wealthy earth mother and become good friends. You might meet people just like you and not particularly get on.
I wouldn't necessarily have met these people in any other way but I can honestly say that over a year in they're some of my best friends. We talk all day on a Facebook message group which started as a night feed support chat but now involves us talking about any crap that comes into our heads. Now we're all back at work we still meet regularly on days off, and go out for dinner and drinks just the mums every couple of months, taking it in turns of who drives and who gets pissed!
The NCT classes weren't particularly illuminating but I would spend that £250 again in a heartbeat for the people I met. I had an amazing maternity leave because of them, and never really experienced the loneliness or boredom others talk about.
Whether you do NCT or not, there will be lots of other opportunities to meet people eg classes at children's centres. They can be pretty cliquey but I found that approaching complete strangers with "oh she's gorgeous, look at her lovely little hat! How cute. She looks about the same age as mine! How's it all going?" was always enough to break the ice! Ultimately new mum groups are a bit like freshers week at uni- you meet loads of people, exchange numbers, add on Facebook, meet up then slowly disengage from people you're not that bothered about and hopefully end up with a core group of good friends. My parents are going on holiday with their NCT friends this weekend, 30 years later!