If you are looking for brand name frames, prices may not vary a whole lot. However if you are looking for normal frames, I can tell you that a standard pair of wire frame glases, complete with assessment by the optician and precription lens starts at USD30-40. That's how much my mom pays despite my constant nagging to get a nice pair of glasses. I think in general you can expect that USD50-80 will get you a good pair of non-brand glasses. Cheaper in M'sia, without a doubt. I've visited malls in Johor Bahru and they are littered with shops catering to the Singapore market. No idea of prices though.
If you want higher quality goods, you can try the Paris Miki shops - that's where I get my glasses made. They often have sales, and are a Japanese company. Most of their shops are also staffed by a Japanese manager, and the service is impeccable. They can have your glasses done same day for certain lens, otherwise some of the lens are manufactured in Japan so turn around time will be longer. I got a pair of high-index, scratch resistant glasses with Gucci wire frames for about USD150. This was during a sale where I got the frame for half off (~USD80).