Custom credit pack size
Most sites have predetermined credit pack sizes which means that you will likely have to buy more credits than you need. A few sites allow you to buy a custom pack size allowing you to buy exact number of credits that you need. There might still be upper and lower limits that can be bought so make sure you look into the details for the sites shown below.
Sites with this feature
123RF
A stock photo platform that offers a wide range of photos, vectors, and illustrations for various creative projects.
Dreamstime
A stock photo platform that offers a vast collection of high-quality images, vectors, and illustrations for commercial use.