spotting scopes can be useful and you can get publication-caliber images from them with practice (just check the birdwatching magazines). The downside is the lenses are relatively slow (F8 or slower) so they are useful in good lighting conditions but not nearly as good in marginal conditions. They are manual focus, and setup/use can be cumbersome and doing it well can require practice. The manual focus and slow speed mean they are useful primarily for stationary or mostly stationary birds. Since most birds aren't stationary most of the time, you are going to be trading off time setting up for a shot and being patient for the bird to step into the frame against a more flexible lens that might lend itself more to catching the bird in action.

The images are going to be softer, too. The lens quality just isn't up to the top end lenses, although on the higher end the quality is quite good.

So, cheaper, but slower, less flexible, and softer. And sometimes, it's the only way to get the magnification needed to get a shot without winning the lottery and hiring a forklift... it's a viable option, but realize that if you research the guys getting published using scopes, their rigs are probably closer to $3,000 US than $1,000. I don't think I've seen a scope i'd consider capable of publication quality images for under $1,000 US, although if everyhing goes just right, you might get one here and there. But predictably?