Most of the information relating to current market situation is not free. Seafood price can be very volatile, it can fluctuate quickly and continuously depending to various factors that are so complex to be predict exactly. For example, natural sources of shrimp may be off-sea of America, Indian, Pacific Ocean... or cultured widely in countries in South and Southeast Asia, in Central America and quantity can be affected by weather, diseases, government policies, market trends and farmers actual actions in deciding their farming cycles, species etc.
One example for the commercial data of shrimp price, market trends and stastistic data is from Unner Barry (http://www.urnerbarry.com/). They supply market information and data for many products such as shrimp, meat, seafood, poultry, egg etc., and this is a reliable commercial source cited by many people in the industry and in media. Some other sites of this category are Intrafish (www.intrafish.com/), FIS (http://www.fis.com/). These sites have rich sources of fishery market information in general and shrimp in particular.
For the commercial sites, you have to register to be a member with annual fee usual paid directly and preferably by credit card. You will have an account set up and can access the information when log in.
Free data however is also available in some government agencies. Although it is not so rich and versatile as commercial sources, it is worth to look at as a reference indications.
1. Shrimp Market Data by NOAA (http://www.st.nmfs.noaa.gov/st1/market_news/index.html)
This site gives information on shrimp market price of New York (weekly) and Boston (some daily), landing quantity, import - export quantity and some even in Japan market. Worth for your checking.
2. FAO fish market information (http://www.globefish.org/homepage.html)
Various information relating seafoods can be read in this site. Some data however you can see if you are registered member only.