Ok, do me a favor, point out how exactly the F-15EX is "far better than Rafael"..btw, it's Rafale and not Rafael.
I will agree with you on the cost aspect..with an expected unit price of $100 to 120 million (fly-away cost and not program cost) the F-15EX will be as costly as Rafale when it comes to unit price, but since India already has spent so much on Rafale infrastructure (support, training, repair, overhaul, etc.), buying more Rafales will be cheaper than F-15EX, for which all of this expensive infrastructure costs will have be spent again.
Also, as you rightly said, with 270 Su-30MKIs, the IAF already has a large number of heavy fighters, whose operating costs are very high. Inducting 114 more heavy fighters doesn't seem to a good option. F-15EX's operating costs will also be very high, certainly much higher than that of Rafale.
What the Air Chief Marshal said in an interview was that since the cost of 114 MRFAs does not need to be spent at one go, it'll be affordable, since payments will be made over time, like 7-8 years or more. The IAF's capital expenditure budget will be able to manage that is what he claimed.