A lot of the sellers on ebay claim that their machines are heavy duty, even though they're not. But heavy duty machines are usually required only for sewing on leather, canvas, or something similar.
Out of curiosity, I just made a sandwich of 8 layers of quilting cotton and tried sewing through it on my Bernina 440. No problem. So I folded it over - 16 layers - and still no problem. So I folded it again - 32 layers - and still no problem. I might try folding it again, but I can't, and even if I could it wouldn't fit under the foot. So my advice would be first to try an "ordinary" machine.
BTW, what are you making?