You must have the difficulty you want to run unlocked.

For nightmares 1-69 → $5 per run
Nightmares 70-99 → $10 per run
Nightmares 100-119 → $15 per run
Nightmares 120-129 →$20 per run
Nightmares 130-139 → $30 per run

Running Nightmares until you unlock Nightmare 160 → $150

Leveling a hero of your choice to 60 → $40

Unlocking all Golden Kingpin shards for accessory → $200 

(3-5 days to deliver)