How much is a 1913 Kingston magneto (box and coils) going to cost?
Because you are a first time poster I will almost give you a pass on your question, almost. The magneto is the part(s) built into the engine the make the electricity not the coils. The coils use the AC electricity made by the magneto to fire the plugs. The coils will work on AC or DC.
Most of the major suppliers have coils and coil boxes listed in their catalogs;
Are you looking for new or used and how complete do you need. Rebuilt or as is?
If you are looking for used you might place an ad in the classifieds. Ball park used needs full rebuild maybe 800 to 1500 complete, maybe less maybe more.
You might get away using this one;
Welcome to the Forum.
I see on your profile you have listed a 1921 touring, which would not have used Kingston coils and coilbox, so I am a little confused.
Are you working on a 1913? Other coils and coilboxes used in 1913 include, KW, Heinze, and Ford, so if you are looking for a 1913 coilbox and coils, you have some options.
RV Anderson builds the early boxes and coils. firstname.lastname@example.org