We can use the PV of perpetuity formula as the dividends will be paid for the infinite period of time. But we need to do a small adjustment for floatation cost. Following formula can be applied:
Cost of preferred stock = Annual Dividend / (Price x (1- flotation cost %))
= 8.50 / ( 97.50 x (1- 0.04))
= 8.50/93.60
= 9.08%