There's no doubt that disciples definitely have no money, so after signing this agreement, they can take out a loan to obtain these things.
As for when they can pay it back...
The agreement is relatively lenient, in theory, it's okay to not pay back for a long time, but the interest will continuously compound.
It even thoughtfully provides an "optimal repayment interval," detailing how much to repay at what time for the best overall outcome.
The dialogue options in this game are quite rich, and many dialogues resonate with Chen Tingquan, just what he wants to say.
"Master, cultivating later might need tens of thousands of spirit stones. Isn't that a bit too..."
The Double-door Immortal's face darkened: "Didn't I just tell you? Cultivation is inherently about defying the heavens, and you said you'd be willing to pay any price to become an immortal.
"If you can't even bear a low-interest loan, how can you talk about defying the heavens?