Depends on how handy u are. I did mine myself. Welded -6 fittings to each each of standard fuel rail. Turbosmart fpr1200 (overkill I know) 460 walbro pump, modded cradle to take 3/8 barb to 9/16 JIC (-6) made all pressure lines in -6 an 200 series hose and fittings. Returns in 400 series. Bosch 2000s. No flex sensor as yet, as I will have to upgrade Ecu (e8 to PS1000). You can run without, your tuner will have to account for some fluctuations in ethanol though. Some people don't go this far, I'd say minimum would be pump, fpr, injectors, replace the line from fuel filter to rail (to eliminate that restrictive banjo fitting) and tune.
Mine owes me $1200ish and I have an IOU tune at Mick s Motosports, when I'm ready. Still considering PS1000 and flex Sensor, as this will give me more flexibility and assurance.