Smart Lights It is great to be able to control the light. Make it bright and cold for cleaning or work, dim it and make it warm for cozy evenings. Wake up by slowly increasing the light instead of burning your eyes in the morning with the power of 1000 suns. Even those Philips Hue Kits are not that expensive, but there are even cheaper alternative bulbs out there. Look for Zigbee, they are all kind of compatible.
HomeAssistant Get a cheap thinclient or raspberry pi (~100€). Set everything up. Control your smart stuff with an awesome privacy friendly interface and build automations you couldn't even dream about a few years back (like "Water the lawn, but not if rain is predicted")
robot vacuum Why should i vacuum my house when there is a robot totally capable of doing it?
3D printer Sounds a little bit crazy, but you can buy a 3D printer at ~150€+ and it's awesome to print little custom fixes and stuff for your home. Is there some ugly gap or device somewhere? Print a custom cover. Broke something? Print the replacement part.