It often isn't necessary to buy proper overalls; in the workshop you can wear just about anything you're willing to permanently stain (loco paint does not wash off, and can sometimes soak through and stain more than one layer), and even for driving you can often get away with anything cotton (for fire safety reasons) and vaguely the right colour, which can be obtained cheaply from a charity shop. I have also encountered such annoyances as you describe, though I believe them to be lack of organisation/lack of customer service oriented volunteers (there's also a near permanent shortage of guards and shop staff) rather than a deliberate attempt to put off those who only want to drive. I've never left a line because of disorganisation, as the extra travel to get to a different one would probably waste more time and money in the long run, but I wouldn't blame anyone who chose not to volunteer at all because of it. The obvious choice in North Cambs would be the Nene Valley. There's also the Bramley project, but they aren't actually running trains yet.