Just reading this through and I thought I would share a recent experience on getting hold uber lenses to play with for nightscapes.
I just got back from a trip to kangaroo Island and I took my Canon D60a. As I dont have any Canon lenses (bar the nifty fifty) I rented a couple.
Lens renting was interesting. Rather than spending a Mozza on good quality lenses I wouldnt use much, the renting option was really neat. A good way to do a try before you buy as well, especially if you are looking at some seriously expensive bits of glass.
Now just need to convince the guy at Lenspimp he should carry a stock of vixen Polaries.

as am planning a Hawai trip..
Sadly I only got a couple of hours over 3 nights due to weather gods and my focus was just a bit off but wow, really dark sites along with high quality lenses..well worth it.