Monthly cost values input to Project tasks

Project Balance sheets work well with GanttProject but require task costs be input. Has anybody written a code to support this already. If yes where/how do I attach these to monthly tasks?

What is a monthly task?

@S2SVETS , please explain with a concrete example in GP what do you have, and what do you want to get.
In GP there is also “task cost” with RESOURCE COST, which is the basis to calculate the task cost, if you meant that…