You can go to a travel agenvy and all your succeeding questions will be answered they can advise you what is the best way for you to get your brother a visit visa going to Qatar.

As far as I know its always been a requisite that a tourist must have at least P10,000 pocket money to show Philippine Immigration people that he's capable of taking care of himself on the country that he will be visiting.

The Affidavit of Support will help but as per your salary I think its not enough to show that you will be capable of supporting your brother during his stay here in Qatar, but I advised you to go to a travel agency here, ask the things that you asked here and they will give you better advise regarding your queries.

Goodluck Kabayan...