Unfortunately, they are all mighty expensive down there, although Sept is somewhat off-peak.

In the St James area, there were some really nice places like The Sandpiper Hotel and Discovery Bay Hotel.

Years ago, my family spent time each summer next door to the Sandpiper (individual cottages and a beautiful beach). It can get a little pricey, but worth a look.

http://www.barbados.org/hotels/sand.htm