If you have sufficient resources to create a full node, you can do so and use RPC commands to obtain the same information you would be able to get from a block explorer API.
Unfortunately, Bitcoin Core RPC commands is poor compared with Block Explorer API.
Poor in what way? You should be able to get literally the same information from RPC commands, and can write a script to get the information by making a series of RPC calls to feed in whatever information you are looking for into a database.
There are a number of cloud providers that will give you enough credit to allow you to spin up a VPS with sufficient resources to obtain (and load into a database) this information for free.
You would do something along the lines of setting the results of RPC commands as variables that are fed into subsequent RPC commands, and from there set more results into more variables that are iterated through, and those results are inserted into your database.
I don't see any good reason to pay for a Block Explorer API if you have the skill set to programmatically obtain this information yourself.