The material to build a vertical blind is also cheaper. The vertical consists of an aluminum head rail and pvc louvers (they can also be fashioned from cloth) where as plantation shutters use pre fabricated wood, vinyl, or composite material. A cellular shade is made from a special paper like fabric which is also more expensive than vertical material.
The biggest advantage verticals have over their competition is durability replacement cost. A lot of us have young children or pets at home that often get into our windows or sliders. A cellular shade will not last a day with a dog that jumps on the windows anytime there is a knock at the door. A vertical blind however is made from sturdier material and will withstand a pet jumping on them. If your pet decides to take a bite out of slats, they can be easily replaced by the consumer.
Another often overlooked advantage of vertical blinds is the ability to change out the louvers. If you decide to paint your room, change the decor, or just feel like changing with the seasons, the louvers of a vertical blind can easily be taken out and new ones put in. This is something the homeowner can do themselves and should not require any installation fees from your retailer. Simply measure one of your louvers, or take one down and bring it with you, and tell the salesperson how many of them you need to have made. What other window treatment gives you this flexibility?