Depending on the requirements of your forum this should not take longer than 1 week to make. The software being used on ForoSAP is vbulletin, which can be easily implemented by yourself as well.
The initial cost of the software (vbulletin) is $285, that's why I put the milestone on $290. The rest of the cost goes to design, programming and deployment. Web hosting costs not included.
The only problem is that I don't speak Spanish.