Hi rocky,
I definitely recommend that you visit the Keleti area yourself before purchasing anything. It's extremely run down and a bit of a facelift isn't going to make much difference. The red metro line does run close by but public transportation is rarely an issue in Budapest. Anywhere in Districts V, VI and most of VII is within a couple of minutes of either a tram or a metro. Neither expat professionals nor students will want to rent a property on Garay utca and as this is your target market, you'd be making life very difficult for yourself. In addition, over €2,000 per square metre for this area is crazy. For around €1,300-€1,500 per square metre, you'd get a renovated apartment in the downtown area.
Budapest