Nothing wrong with a cast crank for less than 500HP. I would always prefer a forged crank but it's not the end of the world if you can't afford one. One reason you see higher prices with a kit is because most include final machining, balancing, clearancing, etc. You typically need to have that done when you combine off the shelf parts, so, even though the kits "seem" more expensive, in the long run they can actually be cheaper.