Bundle App for X+Y that looks like quantity breaks

[D_W]

I sell products that require specific batteries to go with them.

When I sell a product, I would like the customer to be able to choose how many batteries to get at the same time, with a lower price per battery the more that they buy. 

I would like it to look similar to the quantity break offers in many of the apps.

For example, on the product page

Product + 1 Battery $50

Product + 2 Batteries $70 (Save $10)

Product + 3 Batteries $80 (Save $30)

There are two solutions which almost get me there.

I can create them as variants, but then it is very difficult to track inventory.

I can create a bundle page, but I would prefer it to be on the product page like the quantity breaks are.

Are there any apps that do exactly what I'm after? I've had a look at many bundle apps but couldn't find any.