It depends on your vacation style and your kids' personalities, but if DH had a work trip, I'm more than happy to just lounge with the kids in a nice hotel. I would find it a stressful to navigate a new city with kids but without DH. Plus, I know my kids would love to spend a couple hours in the lazy river, head back for lunch, watch a movie or read a book, and then head back to the lazy river again. If your kids are old enough and good enough swimmers to not need you in the water with them, then I'd sit in a lounger and have a cocktail while reading magazines or a fun "beach novel" that is an easy read. You can also jump into the lazy river with them, too, but I always had to drag my kids out when they were too young to be left alone as they would happily stay in for hours.
We usually get vacation rentals, so I'm not sure how much a nice hotel resort runs these days. But generally speaking, I try to stay under $300/night for a 2 bedroom. In some cities, it's been easy to stay under $200 and get a decent 2 bedroom in a convenient location but not so easy in very big cities. We generally pay under $500/person for airfare, but we really like to eat so I budget $200/day for food. We don't do tours/activities so almost all of our vacations are under $5,000 for a 5 day vacation.