Many of those are so massive they even exceed the 32K token limit of GPT-4.

That's true but it doesn't need to process the whole bill in one prompt.

For example you could split a 200K token bill into 10 parts that are 20K each, and ask GPT-4 to create a 2K token summary of each part. Then combine those summaries to create another 20k prompt, and ask it to summarize that.