It sounds like there might be a miscommunication. You say you want to use their images, but then you say it would cost $50 to have work done?
Stock transfers are just that. Stock. They aren't editable images that you can add stuff to (for the most part). Many times, they are already printed so you just have to receive them and apply them with a heat press.
It sounds like you are asking them to make changes to their artwork, which of course would require time and fees to compensate for the time spent creating a new image for you. It doesn't sound unreasonable at all.
Or I could be totally misunderstanding things
