This looks like product configuration with a single attribute.
You'll need an attribute that you can "use to create configurable product". We use one called "size" and it has a massive amount of options. "1 kg" and "25 kg" are examples of those options.
When creating a configurable product, you'll be able to select what it's "configurable by". Your attributes that you select to be "use to create configurable product" will show up on the second "add product" step for you to select. (note: you can't change these once your configurable product is created).
Each simple product associated with that configurable product will carry a unique instance of "size" and carry their own price.
Once the product family is set up, you'll need something that switches between the prices on the product page (I remember people using simple configurable products extension, but that might have been added into magento by now).