Best Buy is pushing down the price of the new Samsung S21 series (unlocked version) down further:
S21 256GB: $550 activate on Sprint or $650 activate later OOS
S21+ 256GB: $700 activate on Sprint or $850 activate later
S21 Ultra 256GB: $900 activate on Sprint or $1050 activate later OOS - Available Again
Not sure if Sprint still has the satisfaction guarantee policy or not. If they do, maybe you can activate now and cancel the service later and save additional $100~$250, depends on which phone you buy.