I used Eve-cost. I don’t know if it does PI, but it does Blueprints. I rarely use it though because the profit margin on most of my stuff is pretty apparent. It’s probably more useful to larger corps.
Calculators will never be accurate for prices - they are market driven and fluctuate constantly. For PI, even quantity can be variable since colonies established on a planet by other players will impact your harvest. It’s a PVP game - interaction with other players tends to be asynchronous for those of us in industry but it’s real and it’s what makes the game interesting.