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Not to be unpleasant but every single one of those photos except #4 is a shining example of exactly why you SHOULD spend more on Canon glass. Features like IS and USM are extremely usefull and even more so IMO on BIF photos.
Back to the OP's question. I use a 70-200L F4 IS which you can pick up used around $800-850. (watch FredMiranda.com) I often use it on my XTi with the 1.4X TC and get 280mm not considering the 1.6 crop factor.
In the price/focal range you are looking at;
The 70-300 Canon consumer lens falls nicely in your budget. $550.
The 70-200L F4 non-IS is $580 new and that would be my suggestion as you will get the sharpness and quality of L glass as well as USM with out the expense of IS. You can easily find a 1.4x TC later.
Here are some samples of the 70-200L F4IS with the 1.4x. The first is a 100% crop to show the sharpness. The second is with the 1.4x, no crop, no PP. The last is the 70-200 without the 1.4x TC. Expect the non IS varient to be perform nearly as well.