Here's my experience:
I have a Bernina that I love but the throat area is not big enough for any decent sized top. So I bought a Juki TL1010Q. Much more room and my FMQ has improved. It was money well spent.
So if your budget is $500-600 I would definitely try to get a Juki or one like it. I paid $874 new but you could get one used for less. Sometimes people go from that to a LA and so you may find one for a good price.
It seems that when you get a bigger throat area the prices jump. That's a shame.