I think it's going to be nearly impossible for you to find a machine under $400 unless you look in the used market. There's been a run on machines due to Covid and in many regions, it's difficult to find anything new under $1000. I have a great machine (Brother 1500) that does most of the the things you want, but it is not lightweight. My opinion is "lightweight" and "ability to FMQ" don't really go hand in hand. Before I got my longarm, I found it easier to move a quilt through a heavy machine because it actually stayed put.
I'm not sure what kind of traveling you want to do with your machine, I take mine on retreats, sew days, and on business trips with my husband. I bought a rolling tool cart that my machine fits into perfectly. Makes traveling with it very easy.