Those Tamron lenses that they have attached in the whole thing are pretty junky. I've got the 28-80mm, lets just say I got it for $40, and it isnt even worth that much. It is just a bad lens, really bad IQ at 55 compared to both 18-55 and 55-250 of Canon. The extra filter I bought for it just in case will never go on it because, this lens is just that bad. I assume by examining the build quality, the 75-300 is the same. The 500 isn't even a canon mount.
Just as mikerosal said earlier, go for a T1i or T2i. Not only are they built for consumers and beginners, but they are great small cameras that a lot of people want even if you don't stay in photography long. The 50D is a beast of a camera, not sure if it would be great for starting out as it is a lot of mula.
Plus with the T1i or T2i you can dabble in video, still with great IQ of your pictures and video.