30A can get away with 10GA wiring, but for 50A you're gonna need 8, or even 6 for a long-distance run. The actual thickness and maneuverability of the wire is not that big of a deal (pulling it thru' walls is not much different than Romex 12), but the price will kill you! 100ft of 10-3 will run you around $130 at the homey depot, while 8-3 is closer to $300.