I've been sewing for about 20 years now and I think I'm qualified to give advice on what you need in a sewing machine. The average person will probably only need a machine that has adjustable needle position, basic stitch options, buttonhole, zipper and blind hem foot attachments, easy to use bobbin winder and extra bobbin casings. Make sure the machine is well built, with todays machines, you can get all of this for under $200.
I wouldn't think most people would need automatic threading mechanisms, built-in electronic embroidery system, complex stitches (overlocking or extra embroidery), computerized controls, one-step buttonhole maker or thread thickness options. Frugal5.com is a neat site that determines the best cost effective machines. They claim that the SINGER 4411 Heavy Duty and SINGER 3323S Talent 23-Stitch provide the best value at http://www.frugal5.com/Best-Sewing-Machine-For-The-Money