Flights at this price are available as early as next week and can be found on select travel dates through March 12, 2019. Seats are scarce, but you'll have the best luck departing on Tuesday, Wednesday, and Saturdays.
As an example below, searching AA.com, I found tickets departing PHL on Tuesday, January 23 and returning from LAS on Wednesday, January 29, 2019. Again you'll have to be flexible with your travel dates, but this deal is out there. You can also buy a $90 one-way fare and return to another nearby airport or a different airline altogether with a custom itinerary.
Need a room in Sin City? Here's a whole list of available accommodations for the mentioned dates via Hotelwatchdog.