Z-6 is an awesome quick detailer but it's expensive at $10 for 16oz. I recently e-mailed Zaino and told them I refuse to purchase any more Z-6 until some sort of quantity discount is offered.
Anyways, the next best thing I have found is Optimum Instant Detailer & Gloss Enhancer. Works on paint, glass, chrome, and plastic just like Z-6 and provides pretty good slickness. It's cheap, too...I purchased a 17oz bottle of it and the 32oz concentrate refill for around $15. When I want to refill the empty bottle, I just dilute it at 3:1 (12oz water:4oz product) and I'm good to go.
I also suggest looking into the new XMT Final Finish Instant Detailer....gallon size containers make it very affordable and all I read is good things about it.