although i despise the idea of a v-8 in an rx-7, it can be done relatively inexpensively, depending on if you're doing it yourself or having someone else do it. first of all, the total weight difference is not that much, but the center of gravity is still favorable with a rotary. also, about the 20b swap...that is in a whole nother league of engine swaps. this swap would cost AT LEAST $30,000 when all is said and done. if you don't want to deal with the problems of the rotary, and it's too hard for you to get to know your car and properly care for it, then don't get one. it's really not a problem unless you let it become one. you just have to be knowledgeable about the car, and you should have minimal problems.