Assuming no demand pricing surcharges ("Surge" or "Prime Time"), UberX and Lyft are going to be cheaper than a yellow cab, since they have a similar fare structure without the 2x pricing beyond the Queens border.

The fare estimates for UberX/Lyft are in the $60-75 range, give or take a little. Tip is included with Uber. Additional tip is optional with Lyft, but not expected to the same extent as with a taxi.

Gett (another app similar to UberX/Lyft) offers fixed fares when you book. Currently they're offering a price of $47 from LGA to Garden City on my account (+ tip, and I usually tip 20% with Gett). I don't know if I'd trust them with booking ahead, as they are aggressive about charging wait time. But if there's a Gett car available when you arrive, I'd book them before Uber/Lyft as the fare is likely to be even less.

If you haven't used these serves, I'd be happy to send you referral codes that will give you some credit toward the ride. Just PM me.