I agree with Steve. In order to better answer your question we need more information and this will depend on your needs. If you are only going to use BiaB and RT only then like Steve said just about laptop will work. But if you are going to get into things like better MIDI sounds, pro DAWs, large loops, sound design, etc then you will need a more powerful computer.

Also what else are you going to using on this computer? Things like photography (both saving pictures and using photo software), movie watching, etc, will need a better computer.

Also include in your budget things that you may need for the above mentioned processes. You may need a good mic, near field audio monitors, audio interface, 7200 RPM hard drive, a Solid State Drive, etc.

So let us know what your needs are today and what you might need in the near future.

My guess for a starting point for a Win 10 music generation computer would be 64 bit, and 8 gigs of ram. The included on mother board video is OK as is the 5400RPM HD if you are going to only use BiaB/RT. A computer with a Solid State Drive would be faster for all operations.

When you are at the checkout line and they ask if you found everything say "Why, are you hiding stuff?"

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware