Inexpensive AA battery charger:

www.amazon.com/gp/aw/d/B073W6GH9Y?psc=1&ref=yo_pop_mb_pd_t1

Looks like the prices have gone up, but they have plenty of panels to choose from, and still under $70. These are the two I have:

www.amazon.com/dp/B00OQ0CAW6/ref=cm_sw_r_cp_apa_vkSJAbDCKCGZJ

And with a built in battery:

https://www.amazon.com/gp/aw/d/B077PXSHJF?psc=1&ref=yo_pop_mb_pd_t1

I also got this battery backup that I use almost daily, and I really like it:

www.amazon.com/gp/aw/d/B075GK35FT?psc=1&ref=yo_pop_mb_pd_t1

https://www.amazon.com/RAVPower-Charger-Waterproof-Foldable-Compatible/dp/B00OQ0CAW6

I use these 2 together. When I am not charging anything else both USB can charge the powerbank. I have used these on backpacking trips.

1. RAVPower Solar Charger
2. Anker PowerCore 26800 Portable Charger