Spark plugs are every 37K. I did mine at the scheduled 37 and then again at 60. At 60 I had to pay for that and an oil change and it came out to just under $500.
'13 35i M-Sport X3 | JB4 Stage 1 | BMS Intake | H&R Springs | Gloss black grill | CF Wrap and Coded by me | Recaro Child Seats
'15 M3 DCT AW/SO | RKP Diffuser | P3 | M Perf Spoiler | iND Exterior Trim | Recaro Child Seat