I have seen this question asked by quite a few people, but I haven't seen a great solution yet.
The store I am working on needs an app to create shipping rates but product quantity.
6 bottles=$35 shipping
12 bottles=$50 shipping
24 bottles= $75 shipping
I have tried doing this by weight BUT the store is connected to a POS system API and there is no way to keep it from over-writing the product weight field back to zero (so they would have to add the weights on their 2000+ products at the store level and that is a no-go).
Alternately, is there something that would set a static weight for ALL products (and wouldn't be impacted by the POS system updates)?
Just to confirm; do you ship the bottles as a set of 6?
If yes, you can use our Multi Carrier Shipping Label app that allows you to set rates based on product quantity. You can create quantity-based flat rates so that, when your customer orders 6 bottles, the shipping rate is $35; for 12 bottles, the shipping rate is $50; and so on.
Did you try with this app Shipping Rates by ZipCode?
This app has features that you can set rate based on product's quantity of basic amount as well as surcharge amount.
For Ex: If you want Increase $25 for each 6 Bottles then you can do with this app. see my attached screenshot:
Here, $25 will be added to shipping rate on every 6 item in the cart.
If you need any kind of special requirement with existing features, please take support of app team and they will guide/help you with your requirements.