I've used mowildflowers before for small little bluestem plants and mine did fine. They also sell the seed at 17.00$ a lbs or something like that. Just put mowildflowers in google.... Im not sure what part of IL you are in but try a google search with litle bluestem illinois ecotype or something like that. Otherwise, you can purchase from a variety of dealers. You also need to decide how you want to seed and prepare the seed bed if you have not already done so, it's not a matter of just scattering a bunch of seeds but Im sure you've probably been looking into that already

JFNew, Prairie Moon, Prairie Nursery are good sources for little bluestem, and may have plugs available too. I would search for "native plants" and "Illinois". Your state is something of a hotbed for prairie restoration, and there are probably many sources for seeds and plugs.

Grasses do best with a spring planting. Water them when you plant.

Ten to twenty dollars a pound for seed, and $50 per flat (37 plugs) are ball park costs. Less if you order in the hundreds of pounds or hundreds of flats.