What is the cab fare from LGA to the Marriott in times square
should be a flat fee of $45 or so
most likely 50-60
The cab fare from LaGuardia Airport to Midtown will be around 50-60 USD. However traffic may make it slightly higher. At the taxi stand in LGA ask the attendant for an estimate to your destination to be sure. Don't take Uber and unless you have little luggage, don't take a bus.
At least $50 bucks, BUT traffic is insane at LaGuardia Airport due to construction and the lines for taxis are rather unfortunate. I would recommend sucking it up and taking the M60 Select Service bus (look for the kiosks near the bus stop for ticketing) over to a subway stop on 125th street (look for the Apollo theater and exit the bus there) from 125th you can take the A train down to 42nd street. If you aren't comfortable with the bus then I'd order a car from a car service rather than wait the hour + it'll take at the taxi line. :)
As others have said, taking a cab from LGA is a nightmare for the next couple years (2019 or 20 likely). UNLESS... You are flying in on Delta, then you will be fine. They serve terminals that aren't under construction.
Regardelss of cost or airlinr, you should also consider time to fight traffic. If any time morning or after work, the M60sbs or Q70lga express busses to the subway are bound to be faster into the city. And they still pick up at the curbside at LGA, including terminal B.
If you still have time to rebook, consider JFK or EWR as well and take the train from the airport.
As others have also pointed to, Uber from LGA is challenging at the moment.
Probably about $45-50 to $60 (depending on the time of day...obviously 7:30am--10am and 4:30-6:30pm are rush hour so more expensive due to time it takes to get there. Don't take an Uber from LGA right now. Construction has moved them off site. You can call a car service in advance (like Carmel Car Service or Dial7) for a good rate and you don't have to wait in the cab line. Good luck.