Depending on what you want to see in Belgium, Gent, Brussels, or Bruges are all good bases, you'll get recommendations for all three based on personal preference. Some people here don't like Brussels much and prefer staying in a smaller, more compact city like Gent or Bruges. From any of these you can do short day trips to any of the others and also to Antwerp. I stayed in Brussels and visited Bruges, Gent, and Antwerp in 3 days. Hotels in Brussels can be a little more expensive but there are definitely some good options with good central locations. I stayed at the Hotel a La Grande Cloche which was between two of Brussels' train stations and just a few minutes walk to the Grand Place. Last year it was about $90 for a single but with the better exchange rate to € this year it would probably be less. I'm sure you'll get some good recommendations for hotels or B&B's in the other locations.