English Mark Darts coin op models have monitors in them already, and they can output to a TV as well.
I got mine at an arcade auction for $25. It was non-working when I got it, but I adjusted the power supply, and then it came right up.
Mine works, but it needs a new dartboard assembly, because some of the numbers don't score.
Anyway. Much cheaper to buy a coin op dart board than it is to build one from scratch.