Given the budget constraints, I can’t help but think of the Nikon 70-300ED.* No, it’s not in the same league as the others – but it can produce decent images in capable hands. Learn to shot within it's limits and it will sing.
The most important feature is the low price for good reach. Play with one and decide if it's worth the $200-$250 used price - or $300. new. Many people feel that he "G" version is just as good, but I strongly disagree.
A bunch of basic snapshots from mine before I sold it. All handheld and all images (except one image) were taken with D70's.
http://morrobayphotos.com/Snapshots/
Here is one 300mm I took while sitting on my mountain bike.
