Xpert MTB/RIF is a rapid test to diagnose tuberculosis (TB) and rifampicin-resistant TB. Cost and affordability will influence its uptake. We assessed the cost, globally and in 36 high-burden countries, of two strategies for diagnosing TB and multidrug-resistant (MDR)-TB: Xpert with follow-on diagnostics, and conventional diagnostics. Costs were compared with funding available for TB care and control, and donor investments in HIV prevention and care. Using Xpert to diagnose MDR-TB would cost US$70-90 million per year globally and be lower cost than conventional diagnostics globally and in all high-burden countries. Diagnosing TB in HIV-positive people using Xpert would also cost US$90-101 million per year and be lower cost than conventional diagnostics globally and in 33 out of 36 high-burden countries. Testing everyone with TB signs and symptoms would cost US$434-468 million per year globally, much more than conventional diagnostics. However, in European countries, Brazil and South Africa, the cost would represent <10% of TB funding. Introducing Xpert to diagnose MDR-TB and to diagnose TB in HIV-positive people is warranted in many countries. Using it to test everyone with TB signs and symptoms is affordable in several middle-income countries, but financial viability in low-income countries requires large increases in TB funding and/or further price reductions.