I have a (rarely used) store item for donations that lives as a product in my club's dues renewal category. I originally set it up as a $1 item and the member could set the quantity to establish the magnitude of their donation). I just had a member donate $35 and I just received (as did the 'notify on purchase' email address) 35 copies of the donation notification. Oops! I hope the donor didn't get 35 copies. Oog.

Is there a way to either limit notifications to one per product (not quantity OF that item) or alternatively, to have a store item with an arbitrary cost? 

Please could you provide me the name of the customer in question (or the member ID will do if needed) and the name of the product? I can then take a look for you

Member ID = 22. Transaction ID = id=914.

Product =store/product/97-trophy-fund-donation (Dues Renewal →Trophy Fund Donation) set to admin view only now. 

Thanks!

Are you using the "Custom emails" settings for the individual product? If so it is intended that multiple emails are sent.

If you would like to allow arbitrary donations then there is built in support for donations

Interesting, no Custom emails, but yes Purchase Notifications.

Problem with arbitrary donations for our use is they don't (seem to) allow collecting additional custom fields like a product does. 

Yes, in this case, you (or anyone specified under the Purchase Notifications setting for the package) would receive an email for every purchase generated of that particular package. These emails are unique to the actual purchase itself, even if purchased alongside other purchases of the same package type.

These emails, however, do not go out to the user - they would receive the standard invoice paid notifications, which will have grouped them all together (since those emails are unique to the invoice that was generated, not the purchases themselves).

Thank you, understood. I'll remove notifications and handle organizational routing manually.