depends on what you're referring to as "minnows". Most store bought minnows are chub, pond, or creek minnows (fatheads, chubs, bluntnose) ... usually referred to as "crappie minnows" or "tuffy minnows". Then there's the Shiners & Rosey Reds. Most of the "minnows" you see, around the lights you have out, are probably Shad (gizzard, threadfin) ... especially if they're in a huge school, circling under the light. The long, lean, pencil-shaped minnows, that dart around near the surface, are probably Brook Silversides.
You can cast net Shad - but, you'd have to find a school of them, that were the size you wanted (about 2-3" long). And you'd have to have a good baitwell or special tank to keep them alive in. And you'd have to have a cast net with a 1/4" mesh.
You can dip net Brook Silversides - but you'd need a wire mesh net (window screen) either in a deep cone or deep square head style (bought or hand-made). You'd have to put a light over the side and cruise the banks, at dark, and dip them as they followed the light ... until you have a sufficient quantity to fish with. That may take you a couple of hours....provided your waters have them in it. (Note - you might be able to use a nylon mesh type net, I don't know .. I've only used a screen mesh type, due to the fact that it has very small diameter "holes" and cuts thru the water faster than a "dip net" type of net)
What price are you paying for your "store bought" minnows ?? At $1/dz that would be 120 minnows ... how many poles are baited & out at one time ? Have you tried using a jig (casting, vertical jigging, "vertical casting") in place of one or more of your minnow poles ?? (can you purchase your minnows by the pound, half pound ?? ... they are usually cheaper that way, and you generally get more for the price)
When I used to fish at night, for Crappie, with my Grandparents - (minnows, Silversides, or Shad) - we never had more than 2-3poles apiece out ... and still managed to catch a nice mess, most times. When we ran out of live Shad or Silversides - we cut the dead ones in half and fished with them ... flicking the line, every now & then, to impart a little action to the bait. That worked, to a degree ... but, dead "minnows" were usually thrown overboard (to feed the "little ones" :rolleyes: ) .......... luck2ya ...cp