I've heard suggestions to use solar, but we don't get a lot of sunlight, so I'm not sure if that would work.
I think this assumption has to be fundamentally addressed. Solar doesn't require direct sunlight to work. All it means is a lower power output and more panels.
Eyeballing the costs for 500 feet of copper wire throws some wild costs at $10k to $20k out. You could fit out a home with solar for a similar cost.
Monocrystalline panels have higher efficiency and work better in cloudy conditions. To keep costs down your best bet is to try to order direct from manufacturer or as near direct as possible (for example, aliexpress.com).
Calculate for Worst-Case
Your main calculations are going to be how much sun you get during winter periods on a day with the least amount of sunlight (worst case scenario), using the surface area of the panel plus rating to work out an estimate on power output, then working out the power demand of the lights, plus margins on energy conversion losses, to finally work out how many panels you'd need to keep it powered during operation.
Design the System to Reduce Losses
You'll want to aim for 12v LED lights (12v to avoid any upstep or downstep conversion power losses, LED for efficiency), coupled with a lithium ion battery (cheaper than lead-acid, smaller, doesn't require as big margins on discharge, better energy density), charge controller (MPPT is the most efficient, but you can get away with much cheaper PWM given it's a small project).
Use a Night-Sensor
To reduce power demands further, I'd also advise a light sensor to detect night-time/dark periods to turn the lights on when it is too dark to see, and off when there's natural sunlight to avoid wasting power, and pick batteries able to store a charge sufficient to cover the longest possible night during winter.
Put together these should easily allow you to implement a solar setup.
If you have a nearby river or stream, you could also use hydro. Wind turbines are expensive and intermittent but might be an option if you have good clearance for one.
If the system doesn't produce enough power, worst case scenario the lights don't turn on and you charge on a consecutive day. You can always add more panels and more batteries.