I was recently looking for a column/field level permission tool, but have not found one (tried building one, but wow, super complex to do!). In my search I found a tool by Titus Labs out of Canada (http://www.titus-labs.com/).
It will dynamically set permissions based on a set of rules. These rules can be built based on the column values for a list. They have implemented it as part of Information Management Policy (IMP), a great approach! You can build your own IMP by referencing our course "Programming Microsoft Office SharePoint Server – 50146"
The tools is very easy to use with an install batch file that simply takes the url of where the features need to be installed. It is installed as a solution so all your web fronts ends will end up with the features installed. It is very easy to use and has some nice error checking in it. Check it out and email Charlie at Titus at Charlie.Pulfer@titus-labs.com for a trial.
They built the addin with extensibility in mind. You can add permissions sets that are reusable as well as arrange the rules you want to be applied in a particular order. Nice product, super simple design, easy install!
Chris