Re: Gotta be honest here...
"Im open to suggestions on how to earn circa £150-200 a month without anyone having to pay a bean."
TL;DR beyond this point.
Presumably every page on your site has useful content other than, maybe, navigational pages. So there's nothing difficult about working out what those reading the page are interested in: they're interested in whatever that page content is. So what you need is a way to get businesses who are in a relevant line of business pay a small amount per month for a static ad to take an interested viewer to their own web site. You could try approaching such businesses directly. It could save them money - at the cost to you of some effort - because it cuts out all the middlemen making and distributing the often irrelevant, punter pissing off, bandwidth hugging crap.