Before you pay $900 at the counter: mail-order, copay cards, the cash-price check, and the calls that actually lower the number.
The price at the pharmacy counter is almost never the only price. In rough order of how often they work:
Sometimes the pharmacy's cash price, or a coupon service price, is lower than your copay, especially for generics. Ask the pharmacist to run it both ways. Watch-out: if you pay cash, it typically doesn't count toward your deductible. Worth it for a $12 generic; think twice for a $400 brand.
Your plan's formulary lists every covered drug and its tier. A different drug in the same class may be a tier lower — sometimes a $10 difference, sometimes $300. Ask your doctor "is there a formulary alternative?" Doctors generally don't know your specific plan's list; bring it.
Many plans charge two copays for a 90-day supply instead of three, and mail-order is often cheaper still. For any maintenance medication, this is generally the easiest win.
For brand-name drugs, the manufacturer often offers a copay card that pays most of your share — sometimes bringing a $500 drug to $5. Search "[drug name] copay card." Two catches: they're generally not usable with Medicare or Medicaid, and some plans run "accumulator" programs where the card's money doesn't count toward your deductible. Ask.
If a drug is unaffordable and you meet income limits, most major manufacturers have a free-drug program. Your doctor's office or the drug's website can point you to the application. NeedyMeds.org lists most of them.
If the drug is covered but at a high tier or blocked behind a cheaper drug you've already tried, your doctor can request a tier exception or a step-therapy exception. The Pharmacy Navigator walks through this.
Prices vary by pharmacy even on the same plan, and some plans have "preferred" pharmacies with lower copays. Independent and warehouse-club pharmacies are often cheaper on generics.