DEC's PDP-10 was a svelte, compact computer from the 1960s—it didn't even need its own room, though it was strongly recommended for environmental reasons. Moreover, with an installed-and-running price tag under a million dollars it was cheaper than what you could get from IBM. Now, 60 years on, you can buy an adorable and functional replica kit for $400, though you'll need your own Raspberry Pi to stuff in it.
The PDP-10 was DEC's 1968 mainframe that became the ultimate hacker playground at the MIT AI Lab. The PiDP-10 is a modern replica, in the same line as my PiDP-11 and PiDP-8 kits. Basic soldering skills are required to build the kit. Or yo can choose the Assembled & Tested option. In both cases, you will need to insert your own Raspberry Pi 4 or 5, which runs the simulation behind the scenes! The Pi is not included in the kit.
No refrigerator-sized memory modules or whirring tapes needed—sadly.
PDP-10 replica kit: the PiDP-10 [Tindie]