Then there is ammo price. The price for .223 ammo is considerably more than 7.62x39 ammo is. 1000 rounds of .223 ammo is about $179.00 and 1000 7x62.39 can be obtained from some certain sources for as low as $115.00, you have to be careful to get non-corrosive ammo for the mini 30 though since the 7.62x39 is mostly imported.
As for gun design, they are exactly the same rifle, same reliability and the exact same design. In the end, if you are trying to decide between the two, the only difference in the performance is in the ammo.
There is definitely a deciding factor in that the mini 14 has more modifications made for it, like sights, rail mounts, flash suppressors. The mini 30 has most of those things as well but not as many style options. Both are very reliable rifles.
Both the Mini 30 & the Mini 14 can be found for sale on Gunbroker.com, I personally sold my own Mini 30 on Gunbroker.