The cost of the Feingold diet depends on things like whether the whole family is following the diet, whether you are buying or making meals yourself, where you are buying the foodstuffs from and so on.
In practice, the major cost of following the Feingold diet is usually buying additive-free or low-salicylates foodstuffs, which are sometimes more expensive than foodstuffs which contain these things.
There may be additional costs for any materials you buy (such as recipe books or DVDs).
According to the Feingold Association of the United States website, accessed on 2 July 2013,
“Its not possible to predict how long the diet will take to have an effect since there are so many variables. We can look back, however, and see how others have responded. It is fairly common to see a clear, noticeable improvement in as little as 3 days, but some people take 2 to 3 weeks. A minority of people report that the symptoms temporarily got worse before they got better. A person who is not on medication is likely to have a faster response than one who is (especially if the medicine is artificially colored!).”
There is no consensus for how long someone should continue on the diet, if the trial has been successful. However some people recommend that the individual stays on the diet for life, since it is feared he or she may regress if the diet is not followed.