Historical pattern I've noticed: the best deals come in January (New Year's resolution crowd drives volume, vendors can offer lower margins) and September (back-to-school lull, vendors clear inventory).
Spring deals are mid-tier. If you can wait until late summer, you'll likely see better prices. But don't delay treatment just to save $20-30 per vial — the health benefits of starting sooner outweigh the marginal savings.
Also, most vendors have unpublished loyalty pricing. If you've ordered 3+ times from the same vendor, email their support and ask if they have a repeat customer discount. CompoundPharm gave me 10% off after my 4th order just by asking.