The cost of training an AI model is still quite high as far as I know. However, it is already very useful to be able to use AI for searching in your own local data. I have come across a tool that can be installed locally to search PDFs and other types of documents and that I found to work quite well: https://github.com/BBC-Esq/VectorDB-Plugin
Search in audio should also be possible, but I was not able to test this, since I don't have NVIDIA graphics.
Simply follow the installation instructions, you have to install quite a bit of supporting software and libraries. I had to install several libraries manually because their install timed out or they were still missing after the install script had run through.
Once you have launched the program GUI window, first click "Models" and select one (for the start it doesn't matter that much which) and then click "Download Selected Model". After the download is complete (Watch the console output for status) click "Create Database" and select the model in the drop down box. Enter a database name in the text field. Then click "Choose Files" and select one or more documents. If there is an error message because of lack of access rights, end the program and start it again from a console window with administrator rights. Then click "Create Database" and wait until vectorization is complete. Then click "Query Database" and select the database from the drop down menu.
Now you can enter your question in the text box; then click "Submit Question". The vector database will be searched and one or more text selections (so called "chunks") from the document(s) that most fit your question will be delivered. If you select "Chunks Only" they will be displayed directly, otherwise they will be given as input to a LLM that will formulate an answer from them. You may select an LLM vis LM Studio which has to be installed separately; if you use the selection "Local Model" one will be downloaded if you use it the first time.