If you want cheap bikepacking bags just to see if you like using them, I'd consider borrowing stuff first.
Very much this.
As you ride more, you'll keep re-evaluating what you want to carry, and how to fit it to the bike. I reckon I've tried at least 3 bags in each of the common positions (bars/frame/seat) for both the MTB and the gradventourer, and even now I chop and change depending on how much gear I'm carrying/where I'm headed etc.
I've used the Revelate Viscacha I bought off here on almost every big race. I liked it enough I bought another used one off here for the missus. If I didn't like it initially I could probably sell it for what I paid. Even if I used it a few times, could probably sell it on for same price.
Very much this.
As you ride more, you'll keep re-evaluating what you want to carry, and how to fit it to the bike. I reckon I've tried at least 3 bags in each of the common positions (bars/frame/seat) for both the MTB and the gradventourer, and even now I chop and change depending on how much gear I'm carrying/where I'm headed etc.