Wyeast charges roughly 67$ per litre of common yeast (american ale, london etc) my 5 bbl brewery needs 2.5L per batch under 16 plato (3 trillion cells) and then you can double that for lagers or 16 - 19 plato brews. So a brand new yeast strain for a 10 bbl from Wyeast is roughly $335 (5L)
If you want to make the best beer you can, and i know we all do, yeast health is super important. Whitelabs says that the liquid pack is nearly dead at 4 months - so if you buy 100 billion cells, you likely have 35 billion remaining after 90 days of manufacturing. great site to check is...