Mule Deer has written extensively on the subject of scopes, a topic that he has researched extensively. Before you spend your money, spend a couple of hours reading what he has said about the topic.
Personally, I have had excellent experiences with Swarovski optics in low light situations (primarily hunting leopard).
You might be able to find a good, used Swaro AV or Z3 ~ $500. I would also give the Meopta line a close look (no pun intended).
I've got several Swarovski's that I love but they are pricey. I bought a GPO (German Precision Optic) 4x12x40 several months ago for a 22-250 I bought here on the forum. The rifle still has not arrived yet so I put it on an old .270 just to get some range time out to 200yards in low light conditions. Glass was very clear late in the evening. Impressive and I'll certainly buy another as the price is very reasonable (about 350 ). OBTW I purchased the scope from cameraland!
