However, since you're making an underground film anyway, it will be more beneficial to spend your time making sure your leads are good. Your support cast will probably suck but that is almost to be expected. You want the main people to be the primary focus anyway. A good lead will do an unexpectedly good job of glossing over whatever friends or family you throw in your supporting roles. You would be surprised how many people decide that their underground film should play out in a spontaneous fashion with only a loose rehearsal of the material.
Spontaneity is a good thing when used to enhance a scene or performance.
If you think your story is worth putting on tape in the first place, give it enough respect to have your actors prepared to perform. None of this is a guarantee that a particular feature will work. There is still every possibility that your film will be worse than atrocious. However, it is better to make a bad film that has decent acting, acceptable cinematography and doesn't bankrupt you than to create an outright pathetic feature that lacks any redeeming value. Even the worst filmmaker has to have a little sense of pride.