Handi quilter 5' quilting frame
 

It is the carriage that travels on the frame tracks ( assuming that's what is being called the tray) I would visit the Handiquilter web site and find out if the handlebars can be attached to your machine. I have an Avante the handlebars are bolted to the machine and the machine fits the carriage. Handiquilter has great customer service, they can answer your questions.

No, that wouldn't work. You'd need to add some way to control the speed of the machine. The HandiQuilter is attached to the carriage and handlebar controls. There's a "SureStitch", that's made by The Grace Co, that you could add, but it's about $350 - $400, and is made to attach to a Grace frame and carriage.

I have an HQ Simply Sixteen on the 5' Little Foot frame, and I also have the JUKI F600 sewing machine which is the same body as your F300. Imo, the F series machine would not work on the frame because of its small harp space, if for no other reason. The take-up pole requires space in the machine's harp, leaving you little, if any, room to quilt.
I don't know if there are carriages available to accommodate non-HQ machines for this frame.

Thanks. I think it's too risky. I may need to purchase another machine with a frame to use for quilting instead of finding a frame to use for my machine. I really want to start quilting my own quilts, but don't like moving the fabric. I prefer to move the machine.

What would you recommend for machine and quilting frames combos's for $2k or less? I would love it to have a stitch regulator.

If you are up for payments, Sewing Machines Plus offers 0% financing. That is how I got my Tin Lizzie. I think you will be hard pressed the find anything other than a short arm for under $2k. And there is a reason there are so many short arms for sale on Craigslist. I recommend either saving a little longer, or financing either a mid or longarm.

Thank you for your advise. I never thought of it that way. There are many short arms listed on the resale market but few if any mid/long arms.

I bought my HQ Simply 16 with the little foot frame last year. It has been perfect for me to learn on. I don't have room for a larger frame. HQ does have great customer service. I think it would be unwise to purchase a frame without the specific machine it is built for.