If it´s a trustworthy seller, eBay is a good source, I always received what I expected.
Lens for &400 – for indoor sports as well as for portraits you could use Tokina 50-135 f/2.8, however for outdoor sports (football, car racing, etc.) it will be too short.
If you shoot outdoors, you could also consider the Canon 70-200 f/4 L.