October 15 to December 7 is the window to enroll in and change a Medicare Advantage health plan or Part D drug plan. These have no underwriting and anyone can be enrolled. To find the low cost Drug plan for you, click this Medicare website link. You can select your drugs and pharmacies to compare plans. You will be shown a list of plans (be sure to click "show all") sorted from lowest estimated annual cost to highest.
https://www.medicare.gov/find-a-plan/questions/hom...
Traditional Medicare with Medigap supplemental plans has its own rules and can be applied for any month.