I agree with the people saying that lowering prices wouldn't necessarily guarantee a much fuller ground, but why not go down another route?
When I was at primary school, North End were really good at offering either free or reduced tickets to kids, including myself. At the minute, junior whites (u8) can get in for free anyway, but there could still be a lot of kids above the age of eight in primary schools across Preston that would possibly jump at the chance of getting their hands on a pair of free tickets (for them and a guardian).
Sure, the club wouldn't be making any money from ticket sales, but I'm sure quite a few of the people attending with these tickets would purchase food and beverages, and maybe even some club merchandise. I doubt the kids would be chanting about Joe Garner shagging their wife and what not either, but it'd be getting bums on empty seats and would have the potential to add a few extra quid to the coffers through the sales of those things mentioned above.
Just an idea. Obviously, to make sure it wasn't exploited, it would probably be best to limit the amount of tickets available to each child.
On top of all that, it'd also show a bit of community spirit on North End's part.
This may very well be a scheme that's still in place, but it's just a suggestion nonetheless.