Concerning the accommodation in Cartagena, Volunteers in Colombia has something for everyone. First of all, there is the possibility to live in a homestay. Living in a homestay means living with a local family. Not only is it really fun to do, you also fully emerge in the local culture and its customs. Besides, you can improve your Spanish, since a lot of people do not speak English on a high level. Volunteers in Colombia offers accommodation in different homestays.
The other possibility is to stay in an appartment. That way you can do what you want, you have a lot of privacy and you can come and go whenever you feel like it. So if you prefer living on your own, having more privacy, then an appartment is the way to go.
Here you can find a clear indication of the accomodation costs.