Some time ago i bought one of the cheap DSO138 Oscilloscopes on Ebay. You can find it almost anywhere in kit or assembled ranging from 15 to 30-35 euros...I bought the kit DIY version.
After building it, I decided to rackmount it, and so I went for some minor modifications.

• I had to replace the power connector and soldered a standard Eurorack Flat cable (it accepts 12 volts without any issue, or so it says in the tiny manual)
• I bought two enclosures on amazon (THIS KIT). If you mount them vertically they have the exact same size of a standard eurorack module. I cut one of the two back covers with my dremel, and made some holes in it in order to screw the oscilloscope on it
• I removed the standard probe and connected a 3.5mm jack to it as an input, and another jack that simply act as a "thru" port for the input