Just swing by your local Meijer or Walmart. If you are healthy and were outside this summer, find one that is around 2,000IU during the winter, and if you do feel down, take 2 a day. If you are unhealthy, stayed inside, or have a history of depression, look for 5000IU, but only take that much when for the winter, and switch to a lower dose for the fall and late spring. I have a history of depression, so I take 2,000 all summer and 5,000 in the winter.

Edit: this one is 2,000IU for $11.20, and will last almost the entire year at 350 servings, or half a year if you need to double up. That comes out to 3 cents a day to ward off depression. So worth it. They also sell this brand at Meijer. https://www.amazon.com/Natures-Bounty-Supplement-Supports-Softgels/dp/B00DYSUQEA/ref=mp_s_a_1_4?dchild=1&keywords=d3&qid=1630306403&sr=8-4