A pack of ten at €65 and a pack of three at €24 look like different offers until you divide them out. The first is €6.50 a seed, the second €8. Every price on this site is reduced to that one number, because it is the only way to compare a catalogue where the packaging varies and the seed does not.
Why pack size is the trap
Shops price by pack, and a pack is whatever they decide it is. Across the 815 priced offers indexed here, 291 are packs of ten, which makes the ten-pack the de facto unit of the trade and makes every other size hard to place next to it. A three-pack is not a third of a ten-pack in price, and a twenty-five pack is rarely two and a half times cheaper per seed than it looks.
The rule that survives all of it: work out the price per seed before you compare anything. In this index a single seed runs from €1.92 to €18.05, with the median at €7.85. That spread is what the packaging hides.
Where the differences come from
Breeding costs, spread thin or not at all. A stabilised line takes generations to produce, and the cost of that work is spread across however many seeds are sold. Widely grown classics are cheap because the work was paid off years ago; a new cross from a small breeder carries the whole bill.
Seed type. Feminized and autoflowering seeds take more work than simply harvesting a pollinated plant. They need chemical sex reversal, controlled pollination and, for autoflowers, generations of stabilising work. In this index the median regular seed is €5.65 against €8.15 for feminized, though the difference narrows once you allow for the male half of a regular batch.
Where you buy it. The same strain at two shops is not the same price, and the gap is often larger than the gap between two strains. That is the reason a comparison exists at all.
What the price does not tell you
Germination rate matters more than any of this, and it is almost never stated. A cheap seed that fails to sprout has cost you its full price; a more expensive seed from a shop with a replacement policy may cost less in practice. Shipping and payment fees can move a small order by more than the seed price itself, and they are charged per order rather than per seed, so they punish small baskets.
Age is invisible on a listing. Seeds stay viable for years when they are kept cool and dry, and lose that viability quickly when they are not. Nothing on the packet tells you which of the two happened. The guide to storing seeds covers what that means once they are yours.
Where to look
The cheapest per seed list is the whole index ordered on that one number, and deals shows the lowest offer per strain across the shops indexed. Of the 384 strains listed, 267 carry at least one price; the rest are here because the shops carry them, not because there is a price to show yet.