When is Thanksgiving?

TI-BASIC, 15 bytes * 0.75 = 11.25

Tested on my TI-84+ calculator

1129-dayOfWk(Ans+ᴇ4,9,1

Thankgiving is November 29, minus the day of the week of September 1st, where 1 is Sunday and 7 is Saturday. This outputs in the format MMDD.

Test cases: 2015 -> 1126, 1917 -> 1122, -480 -> 1125 have been verified. TI-BASIC seems to use the Gregorian calendar for all dates.

TI-BASIC doesn't support negative years, but this gets the bonus because we add 10000 to the input. Because the Gregorian calendar has a period of 400 years, this doesn't change the day of the week.

PHP, 65 48 42 41 36 (+2 for -F) = 38 bytes

<?date(Md,strtotime("4thuXI$argn"));

Takes input as the first command line argument. Runs with warnings, which are acceptable by our rules. Prints NovDD, where DD is the day of Thanksgiving.

No online link because ideone doesn't support command line args and I don't know of an online interpreter that does.

Thanks to Alexander O'Mara for teaching me a new trick, and primo for a significant reduction

Mathematica, 59 38 bytes

DayRange[{#,11},{#,12},Thursday][[4]]&