At a finished price of about $4.00 per gallon, I'd hardly call Vinegar cheap. But thats retail for Vinegar in CT. Maybe it's cheaper elsewhere.
A finished gallon of RoundUp shouldn't cost anyone $1.00 unless your buying retail.
Either way, as rediculous as it sounds, Vinegar applied commercially to kill weeds is against the law & you could be fined for using it.
Silly, I know, but only EPA registered pesticides that have been reviewed & approved in your state, may be applied for hire. That said, I've seen a few retail garden center type products around here lately that are registered as contact herbicides & claim to be enviromentally friendy. They all stink of vinegar even though each claims to be better than the other. Some contain vegetable oil surfactants to speed the kill. Just what I allways wanted. Salad dressing that wilts the lettuce faster.
You just gotta love America.