@BG
You can buy Sega Mega drives cheaply nowadays.
Also AT games do a mega drive flashback console- they call it the Genesis in the US of course - and IIRC AT games do a flashback now for both markets. I know their Colecovision and Atasri 2600s do not allow you to play your own cartridges, and have up to 100 games pre installed, although only a few are well known. I have a feeling that the flashbacks of the Segas may allow old games to be plugged in.
@ VV
ZX81- wow. There is an iconic machine. I remember the zx81 well, although the ZX80 was much less common and worth a load nowadays in good condition. There is a massive market out there for old tech, but it is always the awful stuff that commands the cash, software and hardware from beginning and end of a machine's life, plus failed machines like the Oric Atmos, Jupiter Ace, etc. I started in the early 80s playing games largely- on the Dragon machines at home, which had extended Microsoft basic, which was lovely to program. About the last time I was enthusiastic about Microsoft really. At school it was BBC and later BBC masters, with BBC basic, but I often got my paws on Spectrum and Atari machines. Back then machines had personality. I have stuck with the Dragon 6809 machines, for nostalgia as much as anything. The 6809 chip had limited 16 bit capabilities, but sadly the graphics on the machine let it down a tad, and the games were often simple 4k games ported over. By the time good stuff came out in droves the company had already gone bust.......