I have written about do it yourself extension tubes before, but I came across this instructable where user BorisKafka basically built themselves a macro lens using a redbull can as a extension tube.  It is an extremely easy instructable.  They took a camera body cap and cut a hole in it.  They then glued a [...]

There is a great article over on DIYPhotography talking about how to make a reverse macro ring for a nikon. Basically it looks like they are taking the end cap off of a lens and a spare filter and gluing them together.

I have some concerns regarding this method:

a plastic/glued connection to hold an expensive [...]