Peter at Blue Ocean Lines in Santo Domingo speaks perfect English and he is an expert on shipping. He is a go-to guy for anything shipping, highly recommended. PM me if you need his number. Their website is www.blueoceanline.com
There is a place halfway between Navarette and Santiago on the right side as one heads into Santiago which has a yard full of them.
No idea of prices nor any other facts.
Der Fish
There are containers fit for shipping and others that were once fit but not anymore, which get used for storage or other types of use.
Also there are different types (size/floor load capacity/load capacity/reefers/etc) of containers, for different types of uses.
Most containers will be either 20 or 40 feet long. Some are extra taller than normal.
The price (if for using as storage) will depend on those elements for the most part and the condition of the unit.
The best place to buy containers for storage in the DR is at Haina. The best time to go shopping is on Saturday for one.