Doepfer

Mikhail,
I would have to echo the opinions
of the other folks. A mini case will
give you pretty limited options

Here's one possibility (prices from Analogue Haven)

the plan b
model 25 mk2 multi-tasking audio processor $225.00
will give you great Ring Modulation, Amplitude
Modulation and interesting distortion options

doepfer
A-119 External Input / Envelope Follower $90.00
This is your imput and can produce CV and gate.

doepfer
A-145 Low Frequency Oscillator LFO $90.00
This can be used as a modulation source
or an audio source.

For power why not use this and build your own case
doepfer
a-100 diy kit #2  $95.00

As you can see, it adds up. This set up doesn't
even get you a filter and before you know it
you'll be thinking how cool would it be if I could
use the envelope follower to modulate the pitch
of a VCO that is Ring Modulating with my guitar.
Don't get me wrong this stuff is fun as hell.
It just adds adds up quickly.
Soy Sos