Well, I just went through this. But my budget was
It would help if you let us know what you wanted in your head unit. What will you NEED, what do you just WANT, and what could you care less about?
Going through all of that for myself, but with a budget of $50 less than you, I got this:
http://www.crutchfield.com/App/Product/Item/Main.aspx?g=300&i=020DXZ475&tp=5684
That is a Clarion DXZ475MP for
The only concern I had when I ordered it was that the Signal/Noise was listed as 80dB. It turns out that is while playing a source, but measured at only 1 watt into a 4ohm load off one of the HU's internal amplifier outputs. I actually run it off the RCA out (front) with the "internal amp cancel" feature enabled, and it is definitely not too noisy.
Also, since my order came with a "20% off your next order" code, my roommate got one for $72. It is a fairly full featured deck. Except for no HD radio, but I don't know if you care about that.
I can add up to 2 6-disc changers, an ipod dock, either satellite radio solution, and a bluetooth adapter to use it as a "hands free" solution for my Motorola "Q" when driving. They passed a law about that last part here, not that long ago, but I still haven't picked up a "hands free" solution for the car. It will also highpass the front head unit amp channels, and the front RCAs. It will also pass subwoofer frequencies out the Rear RCAs. Originally I cared about all that, but I use an AudioControl crossover w/ all outboard amps, now.
Let us know what you care about, and we might be more helpful.