How much does a stretch Hummer cost?

To rent or to buy? What features are you looking for? Too many variables to answer this question accurately.

For a custom vehicle, you need to speak to a dealer.

You can hire one here. Looks pretty cool!

Check out my answer here first

It costs the entirety of your good taste and respectability, both of which must be forfeit to own/ride in a Hummer. In monetary terms? It depends on which country you are in, import duties from the US in many cases, and how good a deal local workshops can give you for the stretching process.