Your requirements are an exact match for a Cotic Roadrat frame. Google it. Cotic deliver the frames all over the world. They're about £300 with a fork. You'd then build it up, or have a local mechanic do so, with your components of choice - which can work out to be a great deal with some ebay bargain hunting. You'd get discs, all the braze-ons known to man, cromo steel, the ability to run 700c or 26" wheels - even the option to revert to rim brakes with 700c. Oh - and the Rat will go single or fixed or take an Internal Gear Hub.