From what I've heard, you'll get a better price at an AI by booking in advance. Walk-ins pay more.
There are a few non AI hotels around... there's a big new one ... I can't remember the name, but it's a recognized "brand". There are also a few independent places, but I'm not familiar with them. I think there might be a list here on DR1 in the PC info.
Another option is renting a condo... but it's still high season and I'm not sure you'd be able to get one for less than a week rental... but who knows... with luck, maybe, especially if one was being rented out by the owner instead of an agent or manager. The thing is, they can be pricey too... especially by the day and only for two people.
If your arrival is next week, you might find a good deal somewhere that has vacancies, since they are unlikely to fill the space at this point. The Barcelo Dominican Beach is right in the middle of "town" so you can walk outside the resort if you want. It's a bit older and smaller than most, but I stayed there a couple of years ago, and it was OK. Not the most luxurious, but also a bit cheaper.
I guess in the end it all depends on your tastes and budget.