A few bottles that let you actually taste the lessons — the polishing axis, the added-alcohol question, and above all the temperature lever — plus the small kit that makes it work. Premium junmai ginjo and honjozo you'll love live in the $20–30 range; a bottle you enjoy beats a pricier one you find boring. Tick items as you go.
Where. A specialist beats a supermarket. True Sake (San Francisco) is the premier US sake shop — it ships, curates by style and serving temperature, and sells a ready-made at-home tasting kit. Japanese grocery stores (Nijiya, Mitsuwa — both well-stocked in the South Bay) have deep selections, fair prices, and staff who know sake. Total Wine & More carries the widely-distributed names (Dassai, Hakkaisan) for a quick grab. Online direct-importers (e.g. Tippsy / Palate Project) fill the gaps.
How to choose (the course in one line). Read the grade + seimaibuai for the style (fragrant vs savory), check freshness (most sake is best young; ginjo/daiginjo within ~6–8 months), and note any "nama" flag (unpasteurized — must stay refrigerated). Then match serving temperature to the style. Price tracks polishing and labor, not your enjoyment — buy the style you want, not the lowest ratio.
If you're building this over time rather than all at once:
The core tasting experience runs roughly $70–120 — and, as with every course, the highest-value "purchases" (#8, #9, #11) are the glass, the thermometer, and the habit, not the priciest bottle. A $25 junmai you love beats an $80 daiginjo you find boring.