Sum calculations in recursive referenced apps

Greetings to all,

I have an App where Items Reference themselves with the purpose of boulding a tree-like structure. Le't s call it SystemsApp.

To each of Items (Systems) in the SystemsApp, can be referenced Units from another,  UnitsApp.

So we end with a structure like (<-means direction of reference):

ParentSystem1<-ChildSytem1..n<-GrandchildSytem1..n <-...

ParentSystem1<-Unit1..n

ChildSytem1<-Unit1..n

GrandchildSytem1<-Unit1..n

Each Unit has a numerical property, price for example. What I need Is a total sum of all prices of all units per system (that is done), but then I would need to make a recursive calculation, which would look like something like this:

Calculation in ThisSystem:

SystemPrice = sum of all Prices from Units that reference ThisSystem.

TotalSystemPrice = SystemPrice + sum of all SystemPrices of All Child Systems Referencing ThisSystem.

It seems Podio disables the use of the "[at]sum of ..." variable in case of recursive references inside the same app. Is there a workaround to this limitation?

Thanks to anyone vor eventual opinion/advice.