Check out this DIY 200Khz oscilloscope sell on Tindie.com
If you’d rather spend even less money—but more time—then there are DIY kits that cost even less. One example is the DSO Shell Oscilloscope kit, listed for around $35. The device features a 12-bit sampling resolution, and a maximum bandwidth of 200KHz. It also has a rotary encoder for adjustments, and as the name implies, a nice housing to protect the instrument’s insides.
DIY 200KHz Oscilloscope – [Link]