That depends...
Are they:
Die-cut vinyl (solid substrate)
Printed with UV laminate
Waterslide-style
or???
Will you offer custom colours?
I am asking only because the type of decal affects the installation and clear-coat process. A lot of modern manufacturers use a thin lamintated adhesive sheet that are easily concealed under a clear coat. In practice, these should be kiss-cut or die cut, but sometimes you have to cut them out yourself. I have worked with all kinds in doing frame restorations and repaints. Any of them can be made to look great, it's all in the application and finish.
That said...I would guess between $10 and $50 per set