I use a JP8000 (pictured above) as my main keyboard/controller in the studio but I need a compact controller for my portable setup. So I started doing some research online and found this article on MusicRadar. They have a list of 8 keyboards that fit the bill. I'm familiar with some of them and they are all under $150. Click the names to read the reviews on each keyboard.
1. M-Audio Keystation Mini 32
2. Korg microKey
3. Acorn Instruments Masterkey 49
4. Alesis Q25
5. Behringer U-Control UMA25S
6. Line 6 Mobile Keys
7. IK Multimedia iRig Keys
Feel free to comment or offer suggestions/advice.
