This could cost anywhere from nothing (e.g. free) to 3-figures (in USD) depending on the specifics.
How many users are accessing the notebooks concurrently (e.g. all 1000 or only a dozen at a given time)? Is there any downtime, i.e. do the users come from the same time zone, so that app can have inactive hours (say it's OK to be unreachable during the night)?
Depending on the specifics, free hosting may be available (e.g. via Heroku, Google Colab, AWS Free Tier etc.).
As far as paid offers go, this is way too unspecific to be answered in a meaningful way. The answer depends on the actual resource requirements (RAM, storage, data transfer, CPU cores), estimated usage patterns (concurrent users), and your location.
TBH, if no commercial interest is involved, just hosting the notebooks on Github or making them accessible via Google Colab would be the easiest option.