Hi Sriharsha,

Mitsubishi makes several OSD chips, (M35060, M35061, M35062) that will allow 17 lines of 40 characters on a television screen. This gives you 680 characters, which is in your range. I've got one running on an 8052, and it's pretty nice. It has a very nice smooth scroll (pixel by pixel) so if you wanted to display more than one screen's worth of text this is an option. With a TV output, you can use an actual TV or a video monitor (LCD, or whatever). It doesn't have the math symbols you were looking for, but looks to have 63 characters that you can write to create your own (this I haven't tried yet). I think the chip was about 10 USD.

This seems pretty close to what you're looking for. Hope it's of help.

Dennis