Probably the easiest approach would be to use a large 7 segment display like
this one. Of course, the colors don't match your specs; there may be an equivalent display in the color you want. The other approach is to use a grid of LEDs to form the digits. The latter approach is substantially more work because of the need to build and wire the LED array. In both cases I would choose to do the majority of the electronics with a cheap PIC processor.
It might also make sense to contact a sign maker, as they may have some existing hardware that would make the job easier -- or, they might have something that already works (or is close to it).
If I were undertaking the job, I'd make a crude estimate that the first approach would take about a day of labor; the LED grid approach would take two to two and a half days of labor (most of the work is non-electronic stuff). Roughly 20-25% would be design time and the rest fabrication time. An experienced EE or technician will probably take less time than me, although I'm fairly handy in the shop.
I can speak from experience from other projects: the killer of decent estimates is the customer changing their minds about what the project should do or work after the design and estimate have been made. The usual thought is "oh, it should be easy to ...", but it rarely is. So make sure you know exactly what you want.