Compost with coffee grounds, fruit scraps, and pine needles can lower pH like you want.
Peat is also a fairly cheap thing to work into your soil for long term acid. If you can get wood chips or sawdust from pine or oak you could put it into your soil.
OH, chat gpt had a nice suggestion of pine bark. This might be simple to harvest in some areas from down trees (where chips and sawdust needs processing). If you find the right carpenter or sawmill, you might have a free source. This source is a bit more sparce since people started creating all of the burn bricks from sawdust and paper.
The product EM1 has helped me, but I don't grow berries. I enjoy that I can stretch out the EM1 almost indefinitely by brewing it with molasses. I use a tiny submersible aquarium heater and a stock pot from Walmart. Then the effective microbes mix that I am culturing goes into a half gallon milk jug. Instead of burping this often, I only fill the milk jug halfway, and then collapse all of the extra air out of the mill jug. I squish the liquid all the way to the top. This provides a huge amount of expansion, taking much less tending to.
I love the squished milk jug trick for culturing effective microorganisms. The last concern is juts a weight to hold the jug so that it's not floating.
This process sounds like a pain, but I enjoy the thought of being able to make more and more of the stuff, similar to how people culture their own yogurt from the last batch. HOWEVER, the guy with the most knowledge about this stuff says that the product from the store is better than he can make, because it's a known quantity. Cultures are going to mutate in ways that we don't know, as it is influenced by many things local to the environment. He suggests not going past a few generations of brewed cultures before starting off again.
The culture you brew is called EM-2, once it has matured. Going to 5 and beyond you start to see slight variences.
But yeah, thanks for joining my mini Ted talk today
Edit to add: it's called Stretching, but the process is also how they suggest you activate the em1 before use. You can use it straight out of the bottle, but this way gives a nice boost.