You might look into the Carolina Outer Banks for somewhere driveable, or as mentioned earlier, the coast of Maine if you want out of the heat and humidity of the South in the Summer. Honestly don’t know if there’s a direct flight to Portland from Atlanta, but driving from Boston’s no big deal. Have fun whatever you end up doing! 
I would be a little hesitant to fly if there is a chance you’ll have to cancel and work. That said, use this link to fare compare dot com’s “getaway map” to see a map of the lowest filed (no guarantee of availability!) fares from your departure city. I see Atlantic City as $108+ and was actually able to find that on Orbitz. It’s $118 with the tax and that’s round trip and direct flight on Spirit Air. Quite a good deal if you can make the dates work and you don’t mind flying Spirit, which is a low-cost airline. When I’m looking for a quick getaway like you are, I start with that map and then see what I can find using the Orbitz Flexible Dates search.
mo50:
Outer Banks are crazy crowded during the summer; the OP indicated a desire to not be in a place that’s “utterly packed.”
I’m not sure it’s quite your thing, but you may want to think about a 3 or 4 day cruise to Bermuda or the Bahamas or similar - leave on Wed or Thurs afternoon, return Sat or Sun morning.
CheapCaribbean.com seems to have a bunch leaving at all different dates in July, for around $300-600 for an interior room, leaving from ports in FL.
Gives you the advantage of having pools, beaches (depending on the ports), a hotel room and some great food for one price. Keep in mind that alcohol is usually extra and is usually pricey on the boat.
Good luck on your search!
Thanks to everyone who suggested things. As it turns out, “NO VACATION FOR YOU!” Well, I may still get to take one, but I can’t go very far.
This kinda pisses me off, as it’s the third damn time this has happened in a row. it’s not work cancelling me out: just life, the universe, and everything. Ah well, I already have plans to take some time off in October.