If I recall .... my medicare is about $104/month.

This does not include part D (drugs).
(we have secondary insurance that pays for both of us including drugs from my husband's pension, however). We have yet to pay any doctor's bills, or the recent ER visit my husband made, because with both insurances everything is covered ..within reason).

I recall that if I didn't file for it within X number of days...I can't recall exactly how many days...the amount goes up.

Things may be different if you are SSDI, and younger than retirement age.

I'd go to the website and check yourself.