if, then formula help for an unknown number

i have a formula i cant figure out

currently cells P4-P9 display $0.00 they are formulated to change as other cells are imputed. cell P13 displays $6,216 (and will stay that way).

here is the problem

on a monthly basis cells P4-P9 will change from $0.00 to a greater number, i want the new "greater" number of each cell plus the $6,216 from cell P13 to be totaled in cell P16, but if any of the P4-P9 cells still show a $0.00 i want that cell to be added with a default value of $2,429 so that cell P16 will show a projected amount only changing as actual monthly numbers are put into cell P4-P9

budget.xlsx