I always make my own Preserved Lemons. It's a simple process and only costs the price of the Lemons. If you buy them ready-made, they are expensive.
Ingredients couldn't be simpler; Lemons, salt, and water. I usually preserve about 6 at a go, and use just half a Lemon when required. This (below) is the recipe I use. It's quick and easy.
Moroccan Preserved Lemons Recipe - CookingWithAlia - Episode 53 - YouTube
Don't worry if your Lemons eventually develop a white streaky substance in the brine; this is normal, and doesn't harm the Lemons. Mine (above) have been made for several months and the brine is still clear.
As Alia says in the video, these Lemons are essential in Moroccan cuisine. I also use them when roasting Chicken; which was what I was doing last night when I took the photo.
p.s. If the link doesn't work, just go to YouTube, and type 'Preserved Lemons Alia'.