When you are working completely on your own you may ignore some of the most persistent costs.
People often enter the independent sphere strictly because using studio money will limit your freedom. If you use only homegrown funding, or even money from your own bank account, you really only have yourself to answer to. This may be so, but even when you are producing a low budget guerilla documentary you will still have costs creep up that you will not anticipate.
When people think of budgets they usually consider high actor salaries, location costs and fees, and special effects, all of which are generally associated with narrative films and not documentary. One of the simplest things that documentary filmmakers overlook is the general costs of transportation. Since you will not be filming on one central location, like a film set, you are going to have to move around. In an effort to get appropriate B-roll, as well as to go to many of the people you will have to interview, you are going to be doing a lot of driving. If you are going to do a nice set-up, including a full three point lighting and possibly even background graphics, you are going to have to take a few pieces of equipment with you. This may end up requiring a large vehicle or more than one. The rising prices of petroleum are not going to make this cheap, so gas is going to be a major concern. This can end up being the most expensive part of your entire film production, so try to carpool as much as possible and plan ahead. You may even have to pay to stay some places, or even rent a location to conduct interviews.
It may seem idiotic that this is not a consideration, but the cost of mini digital video tapes is commonly overlooked. Again, since you do not have to buy expensive 35 MM film stock many producers do not even consider this a cost. Though tapes may only run you four to eight dollars, after you blow through fifty or more it ends up being a major expense. Try to buy tapes in bulk, reuse some old ones for extra B-roll shots, and conserve when you can. You do not want to have to conserve tapes too much, though, because you need to have the freedom to get extensive amounts of footage to choose from.
News footage is going to be great to give a broader, and more spectator oriented, view of your topic. Though they will often relinquish the rights to the video to you, they won’t go get it for free. News organizations still have to take time and look for the footage, organize it, and prepare a way to give it to you. Often times they will not even be willing to do any of this. This can cost as low as thirty dollars and as much as several hundred. The best way to do this is to go to all of the news organizations in town and see how much it would be. Limit the keywords they will be searching by and be as specific as possible. You can also see if they will just sign a document giving you the rights to use your footage, and from there you can go to libraries and historical societies to find the footage.
Over the production period you are going to find even more hidden costs, including other general transportation costs like parking and possible permits. Try to go on the fly as much as you can, but make sure to always record your expenses. If you end up getting some type of financial return for your film you can use these as tax write offs or offer the documentation for financial reimbursement.