You have a BondAmount field. Then you would have a BondCost Calculation field with the following calculation :
Then click storage option and select do not store recalculate as needed
Use Case() function.
Or magic calculation
Bond Amount * ( ( Bond Amount - 15e3 ) ^2 + 35e7 ) / 75e9
I'm sad that only one even number is there.
There's a number of ways to do this but here's a quick calculation that uses the Case function that should get you started:
BondAmount = "$5,000" ; 30 ;
BondAmount = "$10,000" ; 50 ;
BondAmount = "$20,000" ; 100 ;
BondAmount = "$25,000" ; 150
) // Case
Create a new calculation field with this formula, numeric result and it should update when you change the Bond Amount.
Create a reference table, with 3 fields:
BondAmountMin , BondAmountMax, Cost
0 5000 30
5001 10000 50
and so on.
Get the cost as reference value as a lookup via a relationship.
This way you can fine tune your bond costs and no formula is needed