the ua5, especially if modded, is far superior to the ad20.
Honestly you will need to spend significantly more than your budget to get any sort of "upgrade". "Upgrading" to a V3, or a v2,m148,sonosax,psp2,etc->minime,modsbm-1 will cost you 2.5 times your budget.
what are you hoping to accomplish with this change? what don't you like about your current setup?
I'd sell the mics before I ditched the ua5.