I belong to several Online Swap Meets that are Basic (Free) lists on groups.io
They generate considerable message traffic and image storage and will be impacted by the Jan18th price increases.
Some of these lists are large (2000+ members) that are being subsidized by the paid lists.
Retailers and manufacturers are on these lists as they provide free advertising and free web sales postings.
For Sale listings can be compact; one email listing 100 items for sale, or wasteful, a separate listing for each for sale item.
Frequently the Digest  will list only for sale items from one seller, sometimes over multiple Digest messages.

These lists have the resources to upgrade to Premium at the current $220/year but will not have the resources to upgrade in a week to over $1100/year
for Premium.  For now they are happy to be grandfathered as they are using all their Free image storage.

WE have a pricing plan that will take effect in a week; introducing a new fee per subscriber plan and also promulgating target list sizes.
The pricing plan should also state what pre-existing pricing structures will be grandfathered and for how long.
For example :

• Free lists under 100 members remain free for next ten years
• Free lists under 500 members remain free for five years
• Free list under 1,000 members remain free for three years
• Free lists over 1,000 members remain free for two years

And there should be a NEW, separate pricing plan for Online swap meets hosted by groups.io lists.
Perhaps:

• Free swap meets under 100 members remain free for next ten years
• Free swap meets under 500 members remain free for five years
• Free swap meets under 1,000 members remain free for three years
• Free swap meets over 1,000 members remain free for two years

Grandfathered provisions need a definite expiration date if the costs of groups.io lists are to be shared equitably.
And accordingly list owners facing a Premium upgrade in three years can plan ahead
And list owners of High Cost/volume Online Swap Meets can plan ahead as well.

ken