Very nice. What lens were you using?

If you are shooting in low light situations then an image stabilization lens would also be a good feature.

Oops, I thought one of the lenses was $600, the $300 range lens is reasonable.

Yes, the f stop is good measure especially if you really want to isolate your subject. The price difference has to do the with the glass and material used to make the lens. Obviously the more expensive the lens the glass and materials will have a higher quality. So it is really what you want to spend, what level of photographer you are, and the features of the lense. Unless you are a professional you don't need to spend $1600, you also don't want to go cheap so the medium priced lens would be what I would pick, although $600 is still pretty expensive. Are these Canon lenses, if they are you might try some of the other lens brands, Tokina, Sigma, etc. you can still get a good quality lense from these other brands. Good luck.