We stayed at Hotel Mignon in Naples in January 2013. We had no reservation, and we just picked this one because we were too scared to roam around rough downtown Naples. Location is just around 100 meters (300 feet) away from the main rail station, right across the street.
The downside: reception staff is a bit rude, they don't issue invoices, receipt is a stamped handwritten note, toilet bowl has no seat, bathroom and room weren't cleaned for the whole period of our 3-night stay, cheap bathroom towels are non-absorbent, wrong keys are often handed out to guest - someone tried to get into our room in the middle of the night by using a wrong key and late one night a guest was locked out of the building and had to holler to be let in. Plus, breakfast is not offered.
The upside: for 50 euro per night, it was an adequate option. Location is excellent, you just walk across the street and you get to the rail station. This neighborhood is very, very run down, filthy and dangerous, so it's best not to hang around the streets. The hotel has been redecorated recently, so they're making an effort to improve. There's TV and AC in the suite and the place is reasonably clean.
If you're on a tight budget and have no reservation, this is a convenient option.