curl https://api.v2.dealmachine.com/v1/mail/campaigns/a1b2c3d4/cost-estimate \
  -H "Authorization: Bearer dm_sk_live_xxx"

{
  "data": {
    "recipient_count": 150,
    "price_per_card_cents": 72,
    "total_cost_cents": 10800,
    "total_cost_dollars": 108.00,
    "wallet_balance_cents": 25000,
    "wallet_available_cents": 20000,
    "can_afford": true,
    "auto_reload_available": true
  }
}