What about the original ZX80?
I was into electronics and working as a programmer on B800 computers using the long forgotten and little known language MPLII. I'd been taking an interest in the possibility of getting a home computer, most were far too expensive so I'd decided to buy the Sinclair MK14 (hex keyboard, machine code, one line LED display, 256K RAM). I went to WH Smith for my monthly electronics mag (Practical Electronics, March 1980) to find the regular Sinclair MK14 ad and order it for a budget-stretching £40 (about a weeks pay at the time). Instead of the MK14 there was an ad for the ZX80 at an even more eye-watering £100 but only £80 in kit form. The specification (1K RAM, BASIC, QWERTY, used a TV as display) was so much higher than the MK14 that, despite the price I had to have one and could stretch to £80 if I cut down on a few luxuries like food.
The kit wasn't the easiest project with hundreds of densely packed solder joints but I'd got the experience from building a Sinclair scientific calculator and before that the Micromatic radio.The next problem was what use was it! The Sinclair hype read: "You could use it to do quite literally anything from playing chess to running a power station." That proved to be something of an exaggeration!
More than half of the massive 1k of memory was used to map the screen if you wanted a full screen display (24 lines of 32 column one byte mono characters) so we were left with around 384 bytes for the program. I claim to be the first to create a playable game in Sinclair BASIC using all but one byte of the available memory. It was a kind of fox and geese against the computer, winnable but not without working out a counter intuitive strategy.
As finances wouldn't stretch to the £20 to buy a cassette player I had to retype the code every time. Nevertheless I typed it up and included a detailed explanation of some of the more obscure logic operations I'd used to do some bit-twiddling in the screen memory.
I sold copies of the listing through a small-ad in an electronics magazine attracting orders from around the world. That more than recovered my costs and encouraged me to pre-order the Newbrain computer (initially intended as the BBC computer) but as that project hit problems BBC eventually cancelled and switched to Acorn, so did I. My Acorn/BBC was later replaced by the Acorn Archimedes as soon as it was announced. I was so blown away by the ARM chip that I bought some Acorn shares which were later converted to ARM shares. Around 25 years ago an HSBC investment specialist told me they weren't worth holding on to but luckily I disagreed.