4096-bit dynamic RAM chips were commonly used for main memory in microcomputers of the late seventies. According to the Mostek MK4096 datasheet, it was sold in various speed grades, with the slowest having a cycle time of 500 ns, corresponding to a clock speed of 2 MHz.
That's fast enough to run an 80-column display, if you put the font in a separate ROM off the main buses.
It's fast enough for 40 columns with access interleaved with the CPU. The 6502 could work this way out of the box, which Apple and Commodore both took advantage of. The Z80 could do likewise with a little supporting circuitry to stretch the 3-T-state cycles to 4, though Amstrad was the first manufacturer that I know of to do this.
Were any dynamic RAM chips ever sold in speed grades slower than 2 MHz, such that you could get more memory per dollar if you didn't need 80-column, or 40/interleaved, capability?