DeepDream is not a GAN. So just want to clarify it first. The one sold for half a million in Christie is GAN, not DeepDream. So it is a very different topic and likely you need to train the model with pictures (a lot of pictures) provided by you.
I don’t have a good answer on the tools with the configurability that you prefer. But if you search “neural style transfer online”, there are a few options.
For developers, they may just start with some code available online.