VSTi synths + Midi Controller is in your price range.
Unless you go with something like:
Alesis Micron
Korg MicroKORG
Roland SH-201
That Alesis Micron is probably the best choice. I believe a few guys from here have that Micron synth and like it. Though if your willing to pay a lil bit more, that Roland SH-201 seems bad ass for it's price (check out the video of it on it's website).
I personally like using "software" VST virtual analog style synths like:
FL Studio (Host/VST Plugin)
-Arturia MiniMoog V
-G-media Minimonsta
-Novation V-Station
-Novation Bass-Station
-reFX Vanguard
-Native Instruments Pro-53
-LinPlug Albino3
-Applied Acoustics Ultra Analog VA-1
-Sonic Charge MicroTonic
-Synth1 (Freeware)
-SuperWaveP8 (Freeware)
-MDA JX10 (Freeware)
Check out kvraudio.com if you decide to go the software route. I would say I probably use the MiniMoogV and the MiniMonsta the most, I love the sounds I can get out of it for basslines (some really PHAT stuff), leads and brassy sounding stuff, great for HipHop, RnB style. You can also achieve that classic gangster WestCoast hi-pitched lead sound with those. I also love using Synth1 since it's so easy and fun to mess around with, great sound as well. That MicroTonic is also lovely for synthesizing your bass kicks and other percussion style sounds, you can create some wicked 808 sounding kicks, zaps and what not. The rest of those synths in that list are all awesome as well IMO.