Adding hundreds of fields to a content type in Drupal 6
The one time I had to do something like that (it was a Drupal 6 site) I exported the content type, edited the export manually (lots of copy-paste and search-replace) and imported it back into my site.

That said, a content type with hundreds of fields is going to be huge. I'm afraid that it's going to be a nightmare for your editors, terrible to maintain, and it might hurt performance as well. If I ever needed a content type with hundreds of fields, I would stop right there and start re-thinking my site architecture.