If you can fabricate single-sided circuit boards at home you can build this digital oscilloscope ... end of things with a CPLD used to manage the sampling rate. Data is displayed on a 240× ...

Both oscilloscope channels are protected for overvoltage up to +/- 50 V. The FPGA samples at 100 Mhz through a 10-bit dual analog-to-digital converter ... has a 10,000 sample buffer.