Well, there's three things here.
One, you want to work there, but you need paid.
Two, they want you to work there, but they're tight for cash.
Three, there's a minimum wage in the UK.
It's one of those places that unless you can add extra value, beyond your routine work on site, or you're in a supervisory role, that minimum wage is probably the best they can offer, especially if they're paying by the hour, not the annual (or proportion thereof) salary.
If they offer free accomodation too though, that's often of value beyond increasing your wages.
Would they also pay your fuel costs to come north and go home again ?
I think you might be best to compile a check list of things like those I've mentioned and do some sums.
See what they offer, and work out if it's tenable or not.
Managerial posts will always pay more,
Average salary for Heritage jobs. Check salary trends and pay scale information for Heritage jobs across UK.
www.totaljobs.com
but those aren't the reality of the wages paid to most who work in the sector. Most would love to be offered that kind of salary. The reality is that most who work in heritage do so on seasonal work patterns and on hourly rates. Or they come in to work events, and are paid per 'event'.
Figure out where you fit in, see if you can double up a bit on things, and go from there.
Very best of luck with it
You have done so well to get to this. I genuinely hope it's both successful and satisfying work
M