There can be some variations in the meaning, but the variation is to be found in the implications (connoted meaning), not in the explicit verbiage (denoted meaning). On the surface, the sentences explicitly mean essentially the same thing. But by varying the placement of "please," a different intonation can be used (when actually speaking), or implied when the sentences are written down.
The placement of "please" is not necessary to enable the speaker to create these different implications, but it helps. Using your first sentence, a person can more easily sound deferential, respectful, or formal, by emphasizing "please" prior to saying anything else. Using your second sentence, a person can more easily sound exasperated or demanding, by hammering home the "please" after making the request. And using your third sentence, a person can more easily sound desperate or more deeply in need by whining a "please" right in the middle.
Any of these implications could be created using any of your sample sentences, but the particular placement of words simply has a tendency to fit particular ways of delivering those sentences, and the method of delivering the sentences (the chosen intonation) is what supports the implications. The same effects can be created in print, although it requires a bit of work to make the context support the intended meanings. The syntax alone does not automatically guarantee any particular interpretation.