The price for GarageBand iOS has always been a Yo-YO. I wish, Apple would make upits mind anss tick with one version of pricing.
Initially, GarageBand was an expensive add-on. Then apple switched to giving it away for free with new devices, but users with older deviices had to buy it.
Then, for a short time, they made GarageBand 2.0 completely free, but to get the loops and sounds, we had to pay by an in-app purchase, that gave a lot of trouble. It did not really change the price, because the in-app purchase was as expensive as the app used to be.
Now we have to pay again for the app, but the in-app purchase is free. The price for both together is still the same. 😁
And with an eligible device you get both for free.
Let us know, if Apple Support can help you.