I think it's extremely cool that you're doing this!
Unless you know the boxes won't sit long on the shelf, I'd recommend not storing the batteries in the lights, especially if they are alkaline ones. They can leak and ruin the lights. Sorry, I think I already mentioned.
Being a small community thing like this, it's often possible to get donations from local businesses etc. If the lights might sit for a while before they're put to use, you might consider L91 Lithium batteries. They have a shelf-life for around 20 years, and are not likely to leak. They are more expensive, but that might not be a problem if you can get them as free donations from local businesses.
Both batteries and the lights themselves are often high-margin products, available to the stores at a *much* lower rate than consumer pays. That alone would make it interesting to do a round and talk to people. Both for what you're looking for now, and also to make it known that it'd be appreciated if they'd give you a call if they're retiring any products, and want you to take it off their hands. You could also end up with deal like being able to get batteries at cost.
As for specific products, check out Eveready 1D, and Rayovac offerings. These can be had for $6-$10 for dual-packs. Free would be better off course. If you can find stores selling these, and then either get them for free, or at cost, you're approaching a workable price point.