I agree with James that you should consider the fees that professionals charge. However, there is a baseline cost of work for you below which you should not do the job. Here is how you calculate it:
There are three components that go towards figuring out the value of your work. If you charge below the sum of these components you will be losing money.
- Labour time
- Fixed assets
I'll address these individually, albeit briefly, below. You will need to put some flesh on the bones of this calculation:
1. Labour time
This is difficult to estimate. It is essentially the rate of pay needed to keep yourself in the manner you are accustomed too. This is obviously a subjective measure - if you are giving up an afterschool job to take photos, then its probably the rate of pay from your other job. If you don't have any need for income because your parents cover all your costs then you don't have to value your labour time at all! This is obviously a competitive advantage - other professional photographers not only have to sustain themselves, but often have a family to feed! Its worth noting that for adults there is a socially acceptable minimum standard of living quantified by the minimum wage.
For the purpose of this calculation however, lets assume you are giving up a four hour shift of your after school job to complete this job for which you would otherwise be earning $10 per hour, or a total of $40..
2. Fixed assets
I am assuming here that you will not purchase any durable equipment for a photography job but will instead use equipment you already own (otherwise the calculation becomes a little more complicated, but is still tractable). In this case, the contribution of your fixed assets (e.g. camera, lenses, car, accessories, etc.) is calculated as a proportion of their average lifespan consumed by use. In some cases you can calculate this directly. For example, if you are shooting with a 500D that you purchased for $750 with an average lifespan of 100,000 shutter actuations, and shoot 500 photos for a job the calculation looks like this:
Amount of asset used
Amount of asset in average lifespan
You need to reproduce this calculation for each of your fixed assets. Rather than working this out directly, lets arbitrarily quintuple the figure for your camera body and get a value of $18.75 of the value of your fixed assets consumed by a job.
This is the easiest component to calculate, as you can simply keep the receipts. Lets assume that this job requires $10 worth of gasoline and $20 worth of photo printing.
This gives a cost of consumables of $30.
Value of your work
The value of your work is the sum of these components. In this rather contrived example, that is:
Labour time +
Fixed assets +
= $40 + $18.75 + $30
This is your break-even point, below which you should under no circumstances charge. If you charge less than this amount you will be losing money.
Price of your work
Now, you need not charge your work out at its value. Indeed, you would have no monetary incestive to run a business if you did so. Instead, you need to make a profit by charging a rate greater than your costs.
Exactly what this profit will be depends on market forces. You probably cannot charge as much as high-class professional studios, as they offer a quality of services you presumably do not at this stage. However, you are likely to be the fortunate position (from the perspective of a business owner) that the cost of your labour time is likely to be significantly less than that of your competitors who are presumably raising families, etc. Thus, you are in the fortunate position where you may be able to undercut your competitors prices and thus attract business while still making a profit (at least until your life becomes more expensive, either by getting expensive tastes or leaving home or starting a family yourself).