Honestly, I think the cheap 70-300mm lenses are downright crap. I have the cheapo Nikkor 70-300, non-ED, and I kind of hate it.. although, what more can I ask for the few bucks it costs. I have it if I really need to shoot frames of something further away. The quality however is rather bad.
The cheap 70-300's of all brands are almost the same. The ED doesn't improve the quality much.
If you don't really need the millimeters, then save the money for a better lens. If you're not going to spend four times more money on a lens in a near future, then you don't really have any other options left than the cheapo lenses.
Theres almost no thing that isn't wrong with these cheapo 70-300's. Chromation, distortion, inaccurate and slow auto focus... (especially the bad AF becomes annoying!)
If you can save some more money and don't need the millimeters in the near future, then you could save up for a lens like Sigma 100-300mm F4 or 80-400mm F4-5.6 with stabilizer, which of the both are in range of 1000-1200 bucks. Nikon too has a 80-400mm lens, with stabilizer, but it costs 1600-1700 bucks (with much better quality though).
I'm going to try save up money for Nikon's 70-200mm F2.8 VR lens, it costs 2000 euros.. yipee.. albeit I must first use 2000 euros for an another thing.