GOG's SiN Gold package costs $9.99 and includes the Wages of Sin expansion.
While it can be a bit cliché to say things like "they just don't make them like they used to," there are occasions where the adage is appropriate. Take first-person shooters for example. While the core concept of killing things with imaginary guns is obviously still alive and well, many of the genre's most prominent mechanics have changed drastically over the years. I'm not saying modern FPS games aren't as good as those from yesteryear. I'm just saying (in my most curmugdeonly old man voice) that they don't make them like they used to.
If you want an example of how FPS games used to be done, try heading over to GOG where the retro-centric retailer has just re-released the 1998 shooter SiN. The GOG version is priced at $9.99 and include the complete Wages of Sin expansion originally released in 1999. Dropping players into the role of a futuristic security officer, it sets you on an action-packed and intriguing mission against the corrupt CEO of SinTEK Industries. Gamers who buy the GOG version will also receive the games' manuals along with some other nifty goodies. As with all GOG products, the SiN Gold package is completely DRM-free.
SiN isn't a game you hear spoken about too often these days. That said, it was well regarded back when it first released and if you're up for a slightly more classic shooter experience you might want give it a try. Of course, if you're not sure about SiN there are plenty of other classic shooters available on the site as well.