Hello Susan,
Yes it's true there are a number of costs associated with fulfillment. Costs include Pick and Pack (per order, quantity, data entry, shipping, shipping materials, enclosures), receiving merchandise, storage, insurance, reporting, and some have a minimum monthly fee.
Call some fulfillment houses and asks for costs. With a spreadsheet run some scenarios per possible number of orders per month and compare the costs.
When just starting out, you may compare the costs to doing it yourself. Then when orders are frequent and large enough, either hire someone or use a fulfillment company.
The main thing is that you want to spend more time on marketing activities rather than packing and shipping orders.
Hope this helps you,
Matthew Yubas