Good question. Right now, Westlaw charges something like $100 per search in ALLCASES, which is their database of all federal and state court opinions ever written. Just to retrieve a single document by citation is something like $10.

The general trick is to try to craft a very broad 'initial' search that will encapsulate all of your results; you can create sub-searches within that set of retrieved documents (limited to at most around 3,000) at no additional cost.