I say buy the best you can afford. I LOVE my Bernina 530 with all it's bells and whistles. I also love my Janome 6500 and 6600 with their computerized features. I know that I do a better job of quilting with these over my many vintage sewing machines. I have had NO trouble with them, so do not believe that all "plastic" machines are nothing but trouble....NOT true.
When I have to do really heavy sewing I use my 1960s-70s era Kenmore. These machines are beasts! And they have cams for many many decorative stitches. They have a 1.2 amp motor, which is bigger than any of my vintage Singer machines. I have bought/sold/given away quite a few of these machines and have never paid more than $30 for one. Just be sure to get one with low shank feet, that "homes" (goes to the middle for straight stitch) in the middle and you will be able to use most modern feet.