Are you looking for cheap by Japanese standards or western standards? To be honest, I only have New Zealand to compare to, but prescription glasses and lenses in Japan are a fraction of the price that they are in NZ. I would recommend either Bic Camera or Zoff. The examination is free, you pay for the frames and the lenses are free. If you want special lenses it might cost a little more. With regular lenses, you can get brand frames for 6,000 to 10,000yen. From the Zoff website, it says you can select “thin type” (usugata) lenses for an additional 5,000yen. So you can probably get a decent pair for around 12,000yen I’d say.