For me it was the Radio Shack TRS-80. (My family had every model up to the 4P.) Trying to load tapes to watch a little ASCII man dance in a proto-Dance Dance Revolution? Music, games, synthesis, tinkering—I was hooked.
Even back then, there were computers for people who couldn't afford the more expensive stuff. Take this Tandy, which costs little more than a upgraded Netbook today. From Core Memory, photographed by Mark Richards and written by John Alderman.