I recently bought a house built in the 1960s. It's surprisingly easy to add Cat6 to an older home as the interior walls aren't insulated. I've been adding drops as needed and it takes me about 30 minutes start to finish to run a new drop.
I'm out the cost of materials (maybe $200?) and the price of having an electrician add an outlet to my "MDF"/hall closet ($175).
Dont forget about powerline-to-ethernet adapters, esp if you only have a small number of devices or dont need full gigabit bandwidth. experience varies, but if the two endpoints are on the same breaker, you can get > 100mbps, and if it has to cross breakers, you can (potentially) still get over 1mbs, which is enough for streaming and basic surfing. Much easier than running wire or messing with drywall if you're not handiman-inclined.
I'm out the cost of materials (maybe $200?) and the price of having an electrician add an outlet to my "MDF"/hall closet ($175).