For B12, I get the cheapest vials of Cyanocobalamin from Kawal, who is the contact for DM Pharma:
Wholesaler of Erectile Dysfunction Medicines - 2, Antibiotic, Antifungal & Antimicrobial Medications & Anti Depression, Anti Anxiety And Other CNS Meds offered by DM Pharma Bridge Export from Nagpur, Maharashtra, India
www.dmonlinemeds.com
The B12 is only $1 per vial (and ready for injection). The shipping cost for an order starts at $24. But he sells a lot of other stuff, including retinol creams, generic Voquezna for heartburn, meloxicam, etc.
Almost everything he sells is ridiculously cheap, much cheaper than ReliableRx or AllDayChemist. As AndyPanda has said before, Kawal can also get things not on the website (such as other meds at IndiaMart.com). The heartburn medication I mentioned is one example.
Kawal's WhatsApp: +91 98230 14762