If you are tempted to jump in any Oracle Learning Subscription or just want to buy a certification voucher, you can check Oracle User Group Champions Program for discounts, they are running 25% right now (March 2021). Or you can became member of UK Oracle User Group and get same deal just for small yearly fee.
If you are considering buying multiple vouchers it may be more convenient to buy whole subscription (depending on exams match).
If you are considering OLS, then keep in mind that it may be possible to buy it for shorter term than 12 months with adequate price reduction. So you can get same content and all certifications in 3 or 6 months just for 25% or 50% of full price.
Deduct the price of all certifications you are interested in. Divide this by all courses which interests you and you may agree that it is actually reasonable priced, maybe even cheaper than buying individual exams without any courses.
Let me know if you want to join me and became certified.