Thought this might help abit
I ride an SS myself a Scott sub 50, I bought mine for about 500 Aus dollar (discounted because of a major scratch, originally 600) actually any single speed bike will do, mines a hybrid if your wondering. I'm not really sure how to convert it into your currency.
Scott's got a mountain bike frame and hybrid tires (in between thin road and think mountain bike tires) Built to be quite durable to, it's a commuter bike.
Looking at those fixies that can run single speed too is a good idea, scott and felt have a couple but their quite expensive. That's if your just going to commute on the roads and pavement.