Welcome aboard!
My recommendation would depend on whether you do other sewing (or just quilts), and if you live near a dealer. If you do other sewing, you should get a zigzag machine; if only quilts, straight stitch will do. It's also convenient to buy a brand you can have serviced easily, so see what nearby dealerships carry.
If you only quilt and don't want fancy stitches, I would go with the Juki 2010Q. It's an excellent straight-stitch-only machine, with lots of harp space for quilting. From everything I've heard, it's a high quality machine that will last for as long as you're sewing. I've sewn on one, and it was wonderful.
If you want some options of stitches, you likely won't be able to get the harp space you would with the Juki 2010 unless you buy used. The Janome 3160 is a nice machine with lots of stitches, for well below your budget. It's nice and compact if you go to sewing days away from work. The Janome Skyline S3 is a bit bigger, and closer to your budget. I find Janomes nice an reliable, easy to use, and they usually come with oodles of accessories (presser feet, extension table, etc.).
I personally like Pfaff machines for their IDT (integrated dual feed - so you don't need a walking foot). The Ambition series (essential, 1.0 or 2.0) would probably have something to fit your budget, and the Passport 3.0 is nice if you want portability.
The most important thing is that you're comfortable with the machine. Give one a test sew before you buy, to make sure it will suit you. Does it thread logically? Can you see your work well? Does it sound nice? Does the foot pedal suit your driving style? These are the types of things that are really personal, and can make the right machine for one person the wrong machine for someone else.
Good luck!
