Quick is always difficult; especially if you want to use real native prairie plants. Buffalo grass comes to mind but I'm not sure and don't have a lot of experience with it. In some areas you can buy Buffalo grass as sod which is about as quick as quick gets. Since you need to cover the bare dirt by August maybe you should go with a temporary solution of clover and/or an annual grass that you can replace after the wedding. Even mowed weeds would be something like cover.

How much money do you want to spend?

You really don't have enough time to establish a beautiful meadow in one growing season to be ready for your wedding. Though low maintenance and drought tolerant it would be, once it was established.

Though I guess you could purchase a bunch of 1 gallon pre-grown plants to fill in the area, that would bloom by fall... but at about $5 to $7 per plant, it would be very pricy.

A typical meadow planting from seed takes about three years to mature and really look beautiful.

I have a wildflower meadow planted but it takes months to grow. I did a little research for you and found that you are probably looking for some kind of fast growing cover crop. I saw Buckwheat Flowers (Fagopyrum esculentum) as one recommendation that flowers every 30-40 days.

Are there public gardens nearby available for weddings? You will need a plan B.

If you have only dirt now, it is really too late to plant a meadow. You could try one of the "wildflower meadow" mixes. It will be annual, not perennial but might be ready for August. Do you have a tractor and plow or know a farmer who will plant for you? It will need watering and weeding.

Next year you can plan for a proper perennial meadow -- they take about 3 years to establish.

For annual mix try Aimers.

For a permanent meadow, check out Prairie Moon Nursery, they have good seed mixes and excellent instructions.

If you want a nice place to walk around for the ceremony and reception I think you will need to place sod. I do not think a seeded lawn will be thick enough to hold a wedding on by August. Perhaps if you immediately plant seed and carefully water and fertilize until August you'll be OK, but sod would certaily be better. i'd put the sod down as soon as possible and carefully keep it watered all summer.

For the meadow that you will only look at and not walk on you could find a flowering agricultural crop such as buckwheat or maybe crimson clover. I really can't say exactly what crop might work best, but a farm supply store or ag. extension agent might be able to help. It is not possible to establish a nice wildflower meadow in a short time. After the weddding you could plow the buckwheat into the soil then begin planting the wildflower meadow.

Another choice for flowers would be cosmos, sunflowers, or perhaps safflower. These can be bought in bulk, planted by spreading onto tilled soil, and require little care, and should be in bloom in August. I'd probably choose sunflowers since they are easy to find in bulk - just plant black oil sunflower seeds sold as wild bird seed. You can get large bags as a reasonable price. You will have to till or plow the soil for them to have a reasonable chance of growing well.

Finally, if you are happy just to have something growing you could plant a grain like oats. Grains are easy to grow, look nice ( no flowers but lots of nice even green with perhaps grain heads by August). As with any crop or flowers you'll have to till or plow the ground to get it ready, and fertilize if you want really thick growth.