OFT II
US Veteran
You could hire my wife to take care of it. She can fertilize, water and care for Johnson Grass and it will be dead within two weeks.

The 3 gallon jugs (or 30 gallon barrels) of gly are usually 41%. Roundup super concentrate is 50%.
41% gly is cheapest way out, but if you use it undiluted, expect a 20-24 month timeout of grass and such regrowth.
2,4-d Ester version should solve your problem, but be aware that it migrates in the soil and can harm nearby desirable growth.
I use ester on weedy stuff, and Crossbow diluted 6 to 1 on stumps and wild rose bushes.