I buy Organ brand sharps by the 100 on eBay - about $15. Assortments of 100 in different sizes cost a little more.
They're every bit as good in quality as Schmetz or Klasse', but they don't have the huge variety of different types of needles. (Denim, topstitching, quilting, embroidery, wing, spring, etc.)
I use them in everything from a two-year-old Futura back to an 1894 treadle and I've never had a problem with them in any machine.