I have a friend who bought an inexpensive Brother machine at Costco. That's an option too. I agree with those who suggest buying it AFTER you arrive in your retreat city if that's an option; then you only have to worry about one-way shipping. Also, maybe a smaller machine would fit under the airplane seat if set on it's side...

I had this same dilemma when I flew to a retreat. I bought an inexpensive machine at Walmart when I arrived at my destination. I have an expensive huge Brother machine at home so I packed up my bobbins and other tools and spare feet from my big machine. That way I knew I'd have the 1/4" foot as well as few others that normally do not come with the small inexpensive machines. Plus being familiar with Brother means no learning curve. I did repack it in the original box and checked it as luggage on the plane. That was 3 years ago and it has been on many trips with me, as well as sewing days at church and our community center. If the retreat is in a small town they probably have a Walmart but they may only carry one or two machines. I suggest looking online before your trip for Walmart's near your arrival airport as well as a few others and make some phone calls.

You have lots of good ideas from the others but I just wanted to congratulate you for the win!!!!!!! :)