Here is a thread to get a starting 36" commuter for around 300 dollars.
Here is a link for a decent starting trials/street uni for about $300
http://www.unicycle.com/unicycles/trials/nimbus-20-inch-trials-cycle-13.html/
(they also have these in other exciting colors for about 10 dollars more.)
For things like crank arms, if you want to do some really big riding upgrade to the Kris Holm moment cranks. And if you want to do flat riding with crankrolls and the like you would want the moment cranks with rollo disks, also available on unicycle.com
As for what you have, if you really ride the cx unicycles and start trying to do tricks you will tear them up. The LX can take a little bit more riding but if you dont want your unicycle to fall apart upgrade to one of the ones I suggested.
As for mUni and freestyle, I cant really suggest much, I dont do much myself so I will leave that one to someone with a bit more experience.
That is my suggestions for now.