@brandon is the man on the inside for this
Understand they got quite a bit dosh for a phone mast they had put up and to be fair they are forward thinking in many aspects
I'm not sure I'm much more clued up than anyone else really.
What I do know though is that they've just hosted a rock festival (of sorts) which they are looking to establish as an annual event - they're also advertising now for their upcoming annual fireworks event which has been going for a few years now and seeing how Durham Police stopped their big show up at Aykley Heads I believe Brandon's is the biggest show around so they do very well out of it in terms of attendance and beer money if nothing else.
I've no idea how much revenue that will bring in yearly, but what I would expect is that they'll have got Karl's services for a little cheaper than what another club would've had to pay - he lives in Brandon for a start so the mileage isn't as much as it would've been at Barnard Castle.
All told, these are just my assumptions based on the local knowledge I have. None of it is well informed insider information

.
In terms of finances and the business model, as TVOR mentioned, the top man is very forward thinking and his pride and joy is the ground. Lots of work has gone on over the summer (and continues to go on) as the club are looking to grow. The Boxing Club when it's finished will be great, the view is also for the cricket ground to host more DCCC fixtures and long term the club do see themselves having to be in the Premier League.
However, I don't believe they'll be putting themselves in too much trouble financially, as alluded to, they didn't have a pot to piss in only a decade or so ago and they've built the club up from the verge of insolvency in that time - I doubt that the same ruinous gambling will be taking place and so I would hope that any money being spent is within their means and accounted for.
Again, I'm assuming here, I could be miles off

.