There was never a single global price for Nintendo DSi Point cards. Costs varied significantly by country, currency, and denomination (typically 500, 1000, or 2000 Points). Higher-point cards usually offered slightly better per-point value.
The Nintendo DSi Shop shut down on March 31, 2017. Points can no longer be redeemed for new purchases. Any unused codes are now collector's items only—valuable to completionists, useless for buying games. If you find sealed cards, they're memorabilia, not currency.