Pearls should be restrung regularly to prevent contaminants like sunscreen and skin oils from being absorbed into the pearls.
It costs about $1.50 per inch as an insider trade price, and jewelers do not like doing it. Develop this skill and you will get as much work as you want as well as having the ability to produce your own high value low cost necklaces.
As you can see below, quite a good hourly rate can be had for an experienced worker.
Here is a great article from the British Pearl Association