To use PA plugins on the UAD platform, you have to own the UAD versions of the plugins. Unfortunately, if you want to buy UAD versions of your native PA plugins, there is no "crossgrade" discount. You will have to pay the full retail cost to UA. Those versions are sold through UA's shop, and we have no control over their pricing policies.
For future reference, if you ever want to get UAD and Native versions of any PA plugin, buy the UAD version first and then buy the native version. We will give you a crossgrade discount if you already own the UAD version, but there's no crossgrade if you do it the other way around.
If you have many UAD versions of our plug-ins, you can get the native versions of all of them for only $99. But please note this $99 price cap only applies to UAD licenses that you have at the time of the crossgrade. If you get some new UAD licenses in the future, you can't retroactively apply that $99 to crossgrade those licenses.