Amazon offers Prime members It Follows on Blu-ray / Digital HD for $3.99 with free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $4.98.) Except for the mention below, that's the lowest total price we could find by $12. Update: Note that it's expected to ship in 10 to 14 days.
Note: Best Buy has it for the same price with free shipping.