Are you thinking of scattering these as seed balls? Otherwise I am not sure that you would get great germination by simply scattering seeds on top of an existing meadow without scratching them into the soil somehow.
As to seed type, I suppose it depends what kind of wildlife you want to support. Bees, birds, deer, or ? Also what you already have growing in the meadow and whether it is wet, dry, occasionally mowed, etc.
I would think a mix of species would be ideal. I would be inclined toward perennials. Clover, alfalfa or trefoil might be good in that mix as they would be perennial, support grazing critters as well as pollinators, and probably improve your soil when they die back in winter. If it was my meadow I would be adding medicinal herbs and tea plants, although that would include things that some people would consider weedy, like dandelion, comfrey, nettle, yarrow and mullein. The acceptability of these might vary according to your situation - might not go over so well in a yard in town, maybe fine in the country. Personally I find them all very useful and essential herbs. Depending where you are it may be not too late in the season to gather seeds of many of these, which would keep your costs down even more.