That's a tough one, it sounds like you're already doing everything you can. There's may be some improvements you can make in your post processing, like all of us. It would of course help to get more lens, more pixels, or more closer. [] If atmospheric conditions are already contributing significantly to unsharpness, more lens and more pixels will not have as big of an effect as they otherwise would. In particular, you might investigate digiscoping: mating your DSLR to a long, slow telescope. It's only fast enough in daylight conditions, but if you can live with that then you can get some extremely long focal lengths on the cheap. Just yesterday I was shooting a bald eagle with my 5D2 and 2500mm f/10 dob telescope, which only cost $450 brand new. The biggest downside is how difficult it is to use. (Weighs 30 pounds, sighting, tracking, focusing, etc.) So the very cheapest option is only practical for subjects that are stationary most of the time. There are other inexpensive options that are still portable and easy to use, but not as easy as a real photographic lens, and not as good of image quality either. Search for digiscoping on the web to get started.