Floor Framing Calculators
Span tables decide the member, and the member decides the price. Both calculators here start from the span you have rather than the joist you hoped to use.
There are 2 calculators here: Floor Joist Span Calculator (the smallest joist that clears your span, and what it costs) and Floor Truss vs I-Joist Cost Calculator (the cost difference between floor trusses, I-joists and sawn lumber).
They all work the same way: quantity first, then a waste allowance you can change, then a price built from verified figures and adjusted for your state. Cost is always a range rather than a single number, and every assumption behind it is printed on the page with its source and the date it was last checked.