I have a Janome New Home 124. It weighs 5 pounds and does zig-zag. Some of my friends bring it to sew-a-longs and use it all night. I think it makes quilt a lot of noise, but I suppose you could get used to that. I paid $50 for it less than a year ago. Hancocks has them, and they were on sale sometime last winter.
Maybe you could find a way to use it on your lap if you have a board type table on your lap. You would have to use the foot control.