Month trip to Costa Rica, suggestions?

My boyfriend and I are going to Costa Rica in February for a month. It’s going to be my first trip to the country but he’s visited often. We’re planning on renting a car and visiting a few of his friends that have moved there but he thinks that we should rent a place in Santa Teresa. Does anyone have any suggestions on a good place to stay for a month around the area? Something under $800 close to the beach preferably. We LOVE to surf and will definitely be doing lots of that. Also, any horse places around the area? I’m an avid equestrian and can’t go long without riding :) & good places to dive. Thanks!!