Well - so everyone is aware, "remaining" is not an option. ;-)
Yahoo has declared they are going to stop posting in a month and freeze and then remove all the file storage a month after that. So the group will be moribund at that point.
In answer to the other question I saw, the 100 dollars can be one-time, as long as we are prepared to live within the strictures of the free offering at the end of the year. This includes that, at that time, people have to ask to subscribe (we can't subscribe for them) and that we use less than 2GB of storage for all our "stuff". This later rule will mean we have to impose limits on attachment size especially of images.
I think our archive being mainly text based, including our files, this is something we can live with. We have other spaces for things like wikis and for our code repository.
If all are agreed, I'll float the boat on migration and let you guys help via PayPal, as you see fit - I already carved out the group id (its hidden at the moment). xtrackcad is the group name at the moment - which is the official name of the program since about V4....
Given the sudden rush, it won't surprise me if it takes a few weeks for groups.io to do the needful.