How are you managing billing for AI features when transaction fees are so high?

I'm working on a consumer app that leverages AI for tasks like writing cover letters and grading resumes. Each API call costs between $0.02 and $0.08, but I want to charge users around $0.25 to $0.50 per action. The problem is, the numbers don't add up: for a $0.50 charge, Stripe takes about $0.32 in fees, meaning I'm losing a significant percentage to payment processing on top of my AI costs. Moreover, subscriptions aren't a good fit due to the wide usage variances - for instance, an active user might rack up $20/month in API calls versus a casual user who only spends $0.50. I'm trying to figure out the best approach to billing, considering options like credit packs or monthly usage billing similar to AWS. However, consumers generally dislike unexpected bills. I'm keen to hear how others are solving this dilemmas, especially: 1. What's your billing setup for variable AI costs? 2. Did you create your own credit system or use a pre-existing one? 3. How do you tackle the issue of Stripe fees on small transactions? There must be a more efficient way to handle this, but I'm struggling to find it.