I believe you can take a cab from LaGuardia to the 'N' subway station on Astoria Blvd. which will take you all the way into Manhattan. It makes a stop at Union Square at 14th St. 20th St and first will be about 8 blocks from that point where a cab ride will take about 4 minutes and cost you about $4.00 with tip. From the airport to Astoria Blvd. is about a mile or so from airport and will cost about $4.00 to $5.00. I used to travel this frequently when I lived in Manhattan, but that was about 11 years ago. Hope this helps