Perovskite photovoltaic solar cells and modules can be manufactured using roll-to-roll (R2R) techniques, which have the potential for very low cost production. Understanding cost barriers and drivers that will impact its future. commercial viability can beneficially guide research directions. Because processes, materials and equipment for manufacturing are still under development, it is difficult to estimate these costs accurately. We use a cost method developed to allow for uncertainty in the input assumptions to analyse three demonstrated R2R compatible manufacturing sequences and two potential optimised sequences. Using these novel methods, we have identified and quantified key cost barriers; high cost materials P3HT and PCBM, the use of evaporation for the rear metal deposition, and the transparent ITO coating. We project that technology developments in these key areas would halve the expected manufacturing cost to US$37/m +/- 30%. With 68% GFF, 10% PCE and a 3 year lifetime, such R2R perovskite modules would be competitive with existing flexible PV products in the market on a $/W and power to weight basis. To compete with Si and CdTe in the flat plate PV market, PCE and lifetimes in excess of 15% and 15 years respectively would be required.