Hey @cjroe, i’m not 100% sure i understand.
Does your client want a design for an app or just for the responsive mobile part of an existing website ?
If option 1 :
I would have used adobe XD so my clients could use elements for his app, and maybe i would have done a live prototype on webflow.
If option 2 :
I would have definitely prototyped only on webflow.
About PDF :
Have a look on google, they are a lot of app that can screenshot the entire page of a website, with the width you want etc…
About Pricing :
For my personal work i try to evaluate the time i ll take on the project (4 days for example) and multiply with my daily price.
-> Price range for freelance designer in France for example : From 300€/day for a Junior to 1200€/day for a Senior.
Hope this helps,