I know it seems harsh, but please keep in mind those of us who are recommending it are doing so from personal experience and from professional experience dealing with hundreds of parents like you who have run into the same issue.
I'm going to leave the cost issue alone, and the difference between 10 months and now. I understand where you are coming from, and I don't agree. And, that's fine
I just want to make sure you have the information you need to make the most informed decision you can.
Ok, gate and standard checking. The current statistics state, for gate OR regular baggage, 1 in every 150 bags for whatever reason do not reach their destination or are damaged. Gate checked items get sent down the ramp to baggage. They are not handled separately, and are just as likely to get lost or mishandled. In your case, that will leave you at your destination without appropriate means for restraint for an infant in a motor vehicle, which is much more dangerous than a plane. Mishanding by shipping has a much lower incident rate, but does not get you from the airport to your destination. If you are not personally carrying the seat and installing it into a purchased seat, the next best option would be to have someone meet you at the airport with a seat installed at your destination. That may or may not be possible. If you choose to check via either method, I would pack appropriately in the box the seat came in, take pictures of the seat for potential damage claim, and have a plan B just in case. Unfortunately the best way to get your seat from point A to B is in a plane seat. For older kids, it's as a carry-on. One possible option is the Radian, I think the last I checked it does qualify as carry-on dimensions when folded, but I need to double check that. If not, the safeguard go would be another option. It cannot be used on the plane, but it would stow as a carry-on.
For the plane ride itself, a lap child is an unrestrained projectile. You cannot buckle them with you, since they would be crushed by your body mass. You, being a larger unrestrained projectile, would not be allowed to give your seat to your child in an emergency. The vests are not allowed to be used in takeoff, landing, or emergency situations. In such events, the flight crew will do their best, if they have time, to compartmentalize your child in a blanket, under your seat. According to the FAA, "In nonfatal accidents, in-flight turbulence is the leading cause of injuries to airline passengers and flight attendants." Being unrestrained, your child will be more susceptible. A small bit of trivia, a child under 2 is the ONLY object on an aircraft that is not required to be properly/securely stowed.
Finally, there is the annoyance factor. Not everyone elses, though there is that, but yours. I'm sure you been in a waiting room at your wits end trying to keep a toddler entertained and contained for 30 minutes or so. Now imagine that for several hours. A car seat is familiar to a child, it is something that they accept they are staying put in. A lap is something to be climbed into and left on a regular basis. And your seatmates lap, and the flight attendants lap...
Worst case scenario a temper tantrum/meltdown is a lot easier restrained than unrestrained.
USA Today recently published an excellent article... I encourage you to read it.
http://www.usatoday.com/travel/columnist/mcgee/2008-07-29-lap-children_N.htm
Unfortunately there are parents out there who regret their decision and felt they were not adequately informed. We just don't want you to be one of them.