A cover to get on the street? LOL. A cover paid to who?
Seems pretty easy. The city could do it, Starkville Main Street Association, or the Cotton District Neighborhood Association (assuming they have one) could do it. Whichever entity makes more sense.
Said entity can install some removable barriers across University, basically east and west of where the "action is" in the Cotton District. Every time there is an event, or even every Friday and Saturday night if necessary, set up a perimeter with one or two entrances. Charge a cover to get into the District and give everyone who pays a wristband. All the businesses can agree on some method of discount for people with wristbands.
So say there is a $20 cover, people coming in to actually patronize the businesses and who have no ill will, will gladly pay knowing they will get that money back - plus more discounts - during their visit. If I knew I could pay $20 to get into an area that had good security (paid for by the city/District and the cover charge money) and several fun bars, knowing I'd get a discount on my food and drinks the whole time I'm in there - sign me up.
If $20 isn't enough to stop 24 year old ne'er-do-wells from other areas who are looking for trouble or just a free place to hang out on the street, bump the cover up until it is enough. Hate it has to be that way, but blame the asssholes who can't (or won't) be a part of civilized society.