About you should have negotiated before, quit whining, and similar remarks.
You are missing the point: The employer should be the one worrying, because he is wasting money by the bucket load. If his programmers are constantly distracted by noise, or people interrupting them, their output will be low...but their salaries remain unchanged.
If they have to waste hours and hours because of antediluvian equipment, you still have to pay for these hours. Poor equipment is not only slow, but quite often you have to spend a lot of time to fix it, clean the registry, use some hack settings that are marginally faster, and perhaps more importantly, you force yourself to run only the bare minimum in terms of applications: if it is slow, you try to run as few applications as possible, which means that if you need something from another application, you have to start it. Wastes time and takes your attention away from what you were doing.
All these add up to a lot of wasted time and a much lower productivity. If you save $2000 on equipment and waste 500 hours of your programmers' time, you are a moron.
A second monitor goes for about USD 250. Assuming $50 per hour (for the sake of simplicity) and a 5% productivity increase (on the low side), you will recover your investment within 45 days and by the end of the year, that investment will have paid for itself 7 times over.
Even if your attitude was screw the programmers, I pay them, they are mine to do whatever I want, you still want to get them a proper development environment, because if you don't, it's going to cost you.