Should turn to LR fiarly easily, the bacteria that you need isin the atmosphere, and all the rock is doing is giving surfaces and pores for the nitrifying bacteria to grow on and into. The things you won't get with starting with pure Base Rock is all the cool hitchikers and coralline algae, but you can seed it with a little LR and the coraline should start migrating as long as your water parameters are good.
I figure a trade off of $8.00 per pund vs $2.00 per pound is worth it for me to start with mostly base rock. My coraline has exploded over the past month or so, so there is purple stuff getting everywhere and making it look nice.