To get a free older copy of Xcode that will run on Snow Leopard, create(register) as an Apple Developer at this web site https://developer.apple.com/programs/register/ . You can also turn your current Apple ID into a developer ID by signing in on the link above and following the instructions.
After you create your Developer ID go to https://developer.apple.com/downloads
On the upper left side of the page search for Xcode and just below the search box, uncheck all of the Catagories except Developer Tools (leave that checked).
You will get three pages of results, on the second page you will find Xcode in version 3 for Snow Leopard.