If there's no brass prep involved, material cost for powder and primer shouldn't exceed 60 cents per round unless you're running some novelty stuff. Typically primers cost .10 a piece, a higher end powder charge will be 55gr, estimating $65 a pound (price of IMR powder currently) puts you at .51 worth of powder. It could be cheaper depending on your materials.
Time involved is another aspect. 100 rounds of the same load is faster than 100 rounds of 10 different loads. With everything prepped, using the same charge and bullet, 100 rounds can easily be done in less than an hour. If you're changing powder charges, a couple hours is more accurate. An hourly rate is hard to estimate for you, but since you're paying for skilled services using machinery you don't own yourself, I would estimate $50+ an hour (basically shop rate) would be fair.
Lotta variables, but $100+ is what I would expect for something like that. Subject to change based on any of the variables listed above.