Hotel El Rey is probably the best hotel in La Vega...it's small and fills up fast, but modern, clean, safe and a pretty good deal. There's also a pretty good Tipico Steakhouse across the street with live music at night. I checked out a couple of other hotels, one on the main road called something like "Americana" It looked halfway decent and big from the outside, on the inside it felt like a crackhouse.
If you can't get a room at the El Rey, there are two other good options:
1)Stay in Santiago...it's less than 30 minutes to La Vega and there are plenty of rooms in decent hotels...all around $50 a night.
2)Stay in a Cabana...there are around a dozen large Cabanas between Santiago and La Vega...you could pay anywhere between 1000-2000 pesos (or more if you wanted) for overnight in a very nice, luxury room and head home in the morning.
Also, anyone who hasn't seen it may want to check out the Carnaval in Santiago...La Vega has gotten very commercial and "tigueraje" in the last few years...it can be downright dangerous later in the day and can take you a couple of hours to get out of town after the parade if you're parked in town. Two years ago there were several fights including one with guns fired as we were leaving the parade around 6:30pm.
Santiago is more family friendly...still very colorful and a lot of fun, but much mellower...it's more about the costumes and traditions than getting drunk and whacking each other on the ass. A big difference though is the variety of costumes...in Santiago they have the same "character" costumes, but the large groups are all variations of the same Diablo costume (Lechone), whereas in La Vega, each group represents the Diablo from their hometown, so there are dozens of different themes.