If we set aside the 'retro consoles' that put a Raspberry Pi inside cartridges, gamepads, and old system shells, one of the most popular projects for the mini computer in recent times is the so-called magic mirror. The Web is full of tutorials, and the necessary software is ready to use, but now the official MagPi publication includes a complete guide with the parts list and general recommendations.
A project that adapts to you
One of the best aspects of experimenting with a Raspberry Pi is that it adapts to both the time and the effort you decide to invest. Some projects need constant tweaking, and while many enthusiasts enjoy that, most don't. With the Raspberry Pi you can load the memory card with RetroPie, connect a gamepad, and start playing. From what I've learned so far, the power supply is very important for the Raspberry Pi, and most emulator problems (read 'low performance') come from a source that can't meet the demand. However, what we have here today goes far beyond a retro console. The concept is known on the Web as the 'magic mirror', and the idea is to recycle a monitor and combine it with a two-way mirror (or two-way, if you prefer), using a Raspberry Pi in the background.
The build and the software
The first examples of this excellent DIY project appeared on portals like Reddit, and were quickly imitated around the globe. Fortunately, the magic mirror has reached such a level of maturity that the hardest part is the manual side: building the frame, completely disassembling the monitor, getting a two-way mirror (which can be more or less difficult depending on where you live), and putting it all together. As explained in issue 54 of the official MagPi magazine (link below), the software part is reduced to an installation script and editing a few configuration files, which shouldn't be complicated if you've already dealt with a Linux terminal before. If you need more information, the MagicMirror portal might have what you're looking for.
Honestly, I can't say anything about the final cost of the magic mirror, because it all depends on the initial setup. If your Raspberry Pi doesn't come with WiFi support, you'll need to add a dongle, or accept the fact of opening the mirror every time you want to change something. A monitor can come from anywhere, but most discarded screens have a VGA connector, which in turn requires a VGA-HDMI converter. Even so, I think the effort is worth it. Once finished, the mirror looks great.
