[sassan]

Portrait has a lot to do with light and technique than tools alone.

The difference between a cheap entry level DSLR sensor and top of the notch, super doper mega $ sensor is much less obvious than the level of improvement, expensive glass provides you.

In other words your quality of picture will show a significant difference when you upgrade to those high price lenses. But then you got many good advises here including the last one from Duncan that you really don't need the most expensive ones or for that mater anything beyond the kit lens, until the right time.
When do you know if time is right?
Your eyes will tell you.
Till that time, get to know your gears head to toe and try to bring out all the juice out with what you have now, then as time comes you know how to get the most with least spent.

At the end to address your question with the budget you mentioned, my first suggestion for upgrade would be "Tamron SP AF28-75mm F/2.8 XR". Well you don't get the wide end side but then you get a very useful overall lens with sharpness and excellent color render of this one that is only equal to some much much more expensive lenses. After all you simply can't get all in one swiss army knife type answer.