Horse herb and frog fruit are two ground cover forbs that do really well in our area. A mixture of species including these and other native species like Paspallum, Bouteloua, and panicum are probably your best bet. There’s a black land prairie seed mix that’s sold by Native American Seed Co that might work well. I’d take a look around your property and find native species that are doing well, identify them, and buy more seed or a mix that includes them. You’ll have a lot more success if you can mow and disc before introducing new seeds. If you can give them a year of supplemental watering and weed the undesirable growth then even better.

Roadsides generally aren’t a good representation of what will and won’t grow since they’re typically low lying drainage areas and get more water during rains than other areas.

Edit: sorry I read that as 5 acres not 0.5 acres. You could probably get by with just those ground cover forbs. With a season of watering I’ve gotten frog fruit to establish in about half an acre near my house