Computers often come with modems as part of the package price, and most modems are adequate. All of them will revert to a slower speed if lines are bad. Most are terrible. You might find one you like more. You don't need one to play games and run racing or aircraft simulators, but your kids will look at you funny for months if you don't get a joystick.
Cheap ones are fine for beginners.
The expense comes later, when you have to buy new ink cartridges, so spread the word in your family that those who print excessive copies shall pay the ink bill. It will last for years and its ink costs are one-third the cost of color ink. If you already have a PC or modern Mac at home and are adding a second one, don't be a loner. They'll talk to each other using Ethernet. Cable to hook the computers together is cheap.