One off fee per ORDER, not per ITEM

Good morning

Online store for a trophy company (no current Zencart site)

Now we sell trophies that have engraving which is added per item purchased. Easy enough to set this up.
BUT if a customer wants their logo, we also charge a set-up fee for a logo to prepare it for engraving.
This is only charged once on an order, regardless of which items are purchased.

Does anyone have an idea how to do this?

There was a suggestion of using a gift wrap option, where adding a one time "gift wrap" charge could be made to do the same function.

Any ideas on how to implement this would be greatly appreciated!

If logo is a field/attribute of a product and it is made available to all product and if it is possible that a logo not be included on one product or another (by choice when adding to the cart), then there could be a product that is specific to logo preparation that could be verified as necessary to be in the cart (added if not present or removed if no longer needed) through a file added to includes/extra_cart_actions. Further, the product itself could be controlled to not be available if already in the cart when the product itself is loaded by evaluation of the cart/set as maximum of 1.

The logo could be a separate product with a max quantity of 1. You shouldn't need to do custom programming for this.

Agree for the "simplest" case. It's the additional logic/requirements of ensuring the product is present as needed or when other associated product are no longer present that the customer's experience can be improved.

I believe the wiki has some example code about doing what I suggested about adding a product to the cart if a condition is met and/or no longer applicable.

An alternate approach would be to use an order-total (kind of like the low-order fee) that inspects the order to see if any products include a customer-specified logo and, if so, adds a charge to the order.