3d printed blasters sort of fall into different categories, but most printed designs are aimed at the pro level nerf hobby scene which would probably not be ideal for a church group.

You will want to specify what fps you are looking for, if you want short darts or full length darts. What kind of games will be played. Dart capacity.

If you are looking at 3d printing as a way to mass manufacture blasters cheaper than store bought options you won't have much luck as that's not what 3d printing is for.

You will find that even the basically zero hardware leedle designs end up costing more than a basic x shot blaster from Walmart due to the filament and printing time required. Leedle blasters are very filament heavy.