My experience is that SEN status mileage can be earned for about 8k€ - 10k€ in spend (a bit under 0.01€ per status mile), and discounted A-fares seem to work well if one wants to minimize the actual flying time. I suspect there are some experts here who will tell you it can be done for less, but I suspect it would take a bit of planning and effort, especially with the devaluation of discounted Y and C fares that do not earn full miles.