The length of a film should be directly related to the endurance of the human bladder. - Alfred Hitchcock
First, as a beginning filmmaker, you'll have to make a decision whether or not your script may be too demanding for the beginning director's admittedly small budget.
Stunts and extensive action scenes
Decide whether your story require bike and car chases, helicopter shots, or any other extensive action scenes.
Stunts are time consuming and will add a few more shooting days to your budget. You ought to consider the cost of spectacular stunt vehicles and stuntmen, and last but not least the reality that your liability insurance will skyrocket the moment stunts have been added to the script. The same applies to blasting and destruction scenes.
Decide whether the required special effects too ambitious for your budget. If done inventively, special effects do not have to cost an arm and a leg. So, always try to think natural alternative ideas to replace special effects.
Check whether your script is too verbal. Remember, unlike a stage play, a motion picture is an advanced visual medium. Therefore ask yourself, "Where should I substitute or support verbal expression by the use of visual expression?"
Number of characters
Decide whether you really need a cast of hundreds for your admittedly low budget film. Most likely you will be able to omit or unite some of the characters in the script. Basic concept of the film and it's novel presentation are more important than creating hundreds of characters.
Decide whether too many different and/ or expensive locations required for your film. If possible, just skip any location that demands an extensive travel budget. Try to find an equally agreeable location close to home. If the pricey location will add to the film's production values, by all means splurge on it, but always find ways to limit your use of the location.