Recommendations for Data Visualization solution for large CSV file on a non-profit website
Shiny could be an interesting option: it's an R library which lets the programmer generate interactive web pages from an R program.

All the R libraries for data manipulation/visualization can be used (e.g. the great ggplot2 library for graphs)
The interactive pages are rendered with very little effort required on the programmer side
Very flexible, allows quite sophisticated visualizations (see the gallery) and the result looks very professional imho.
It requires the Shiny server to run on the site, it can be installed quite easily in my experience. There is a commercial version but the free version doesn't have any important limitation, as far as I can tell.

Drawbacks:

I'm not sure I would recommend this to somebody who doesn't have any experience with R, it could be a quite steep learning curve to learn the language just for using Shiny.
It might not scale well with a high amount of traffic, depending on the application and the memory resources.