If you are in this much of a rush then you're going to need specifics - so as a Nikon guy, here is a specific recommendation. I am not saying these are better than a Pentax / Canon / etc etc.. I'm just saying that in my sphere of knowledge, limited to Nikon, this is what I recommend from their range.
Used Nikon D90 or D7100 and start with either the 35mm f1.8G lens, or the older (and awesome) 35mm f2 D (or non D).
Why? Every camera manufacture knocks it out of the park once in a while, and for Nikon the big winners over the years that are great bang for the buck are the D90, D7100, D700 and D3s.
For the D90:
The D90 is an exceptional camera that stands the test of time. It's performance in low light doesn't keep up with todays cameras but there are some REALLY important things going for it.
1) If you work eBay well you can get both this camera and lens recommendation near the bottom of your budget.
2) You don't know what you don't know right now, so that leaves some budget for additional lenses
3) The D90 has a built in focus motor which means it can work with every autofocus lens that Nikon has ever made. The great pro lenses from the early days of auto focus film cameras kick ass compared to even more expensive consumer lenses of today. (D3xxx and D5xxx fail miserably here)
For the D7100:
The difference in price between a used D7000 and D7100 is so close, I recommend the D7100. It's quite a jump from there to the newer D7200, so the D7100 and one of these lenses are within your budget. If you see a killer deal on a D7000 it will do the job too, but the D7100 although now 2 generations behind in the D7xxx series still feels fresh.
It has the same lens advantages as the D90, but also can read the aperture setting on vintage manual Nikon lenses.. and if you're on a budget and really want to master photography this is huge. On the D7100 crop sensor camera a great portrait lens is a 50mm. You can pick up a manual focus 50mm Series E f1.8 lens for under $50 on eBay. That's HUGE.
So - that's my take from a Nikon perspective. Avoid the trap of "entry level" Nikons as you might save a buck or two, but you're trapped into buying latest lenses.. either affordable mediocre consumer lenses or very expensive pro lenses.