You will need to shop around and check photographers' portfolios to find the one that is doing the type and quality of work you would like in your portfolio. Again checking photographers' web sites can help with this. You will want to plan out with the photographer what type of looks you want, what your wardrobe will be, and the costs. In this case, since you are the paying client, you should expect to receive all original film or transparencies. Be sure to work this out before the shoot and be sure what rights will transfer.
Photographers are generally independent business people.
They are free to charge whatever they want for their services. However, competitive market forces tend to keep their prices down, just as the cost of doing business tends to force their fees up. A good, well-run business tends to be busier and able to charge more then a poorly run business. Photography charges will vary in different parts of the nation. Generally, photographers in the largest cities are able to command the highest fees.