I started out with a PE-150 which is your basic bottom of the line machine. It's limited to a 4x4 stitching area, and kind of slow, but you can buy the software for it for $120 or so. Used they run anywhere from $150-$500. They have good resale value. I've owned 2 and never had a problem with either one.
I own both the Bernina Deco 600 and 650 and really like them both. They take the same software as the PE-150, are a little faster, and have a few more features. The stitch outs are higher quality than the comparable Brother machines, don't know how they stack up to other brands. A fair price for a 600 use is $300, a 650 used is $350. Price could be more if a lot of extras are included.
I had a Brother 8500D, which cost $3000 new, and really liked it. I sold it on Craigslist for $1500 used and felt that was a fair price, I had it for 2 years.
I have a Brother Innovis 4000D now, which I paid $5000 for and I love it. I'll probably stick with it and not upgrade further.
My only negative comment is both the Brother 8500D and Innovis 4000D are combo machines, they sew and embroider. I never sewed on the 8500D and probably never will on the 4000D either. I embroider a lot and need an accessible sewing machine that isn't tied up doing something else.