There probably isnt a calculator for items and even if there is one out there it wouldn't be accurate at all due to many reasons:
1) Prices vary from server to server
2) Prices fluctuate over time
3) Rare items can become common over night
4) Inflation or recessions on the market.
5) If drop rate is low/high and demand is low/high at any given time
6) basic SRO economics
