I would imagine they use many different things(Like I recall seeing an interview with the Neptunes on some TV show and they were playing with one of those low end Yamaha synths and an Alesis QS6)... But hands down the keyboard I hear most stuff used from is the Korg Triton.
I know what your saying. I was going to buy a triton but found a used roland xp 80 for $800 and used the rest of my money for an Mpc 60 mk II and a turntable. Just look around and check out reviews on different synths..I don't know much about them so I can only answer from my own personal experience. This keyboard suits my needs.
* the notorious MPC
* the infamous Triton
* the ominous MoPhatt
* the ravenous Motif.
actually, they're all very good pieces of gear, but if you don't wanna sound like everybody else (ok i'm generalizing here), don't buy 'em. my advice: be on the lookout for strange vintage things (like a Korg MS20) and check Sonicstate and Vintage Synth Explorer for price reference & info.
Yo, every synth is a jump off point. The tick is not to use the factory sound set.
Let me lace you with game:
JV's: 4 layer program 2 oscillators per voice (I think)
Motif's: 4 layer program 2 oscillators per voice (I think)
Triton's: 8 layer program 2 oscillators per voice (I think) K2600's: 32 layer program over 100 oscillators (I think)
and that's just the synth engines, not the sampler side.
The Netune more the likely use a custom sound set, so should you. I hate it when I can tell what synth a producer is using.