A
B
1
maxMult
minMult
2
5
2
3
minCost
maxCost
4
$3.00
$10.00
5
6
Cost
Price
7
$1.00
$5.00
8
$2.00
$10.00
9
$3.00
$15.00
10
$4.00
$15.71
11
$5.00
$16.43
12
$6.00
$17.14
13
$7.00
$17.86
14
$8.00
$18.57
15
$9.00
$19.29
16
$10.00
$20.00
17
$11.00
$22.00
18
$12.00
$24.00


In B7:

=IF(Cost <= minCost, Cost * maxMult,
 IF(Cost >= maxCost, Cost * minMult, 
 minCost * maxMult + (maxCost * minMult - minCost * maxMult) * (Cost - minCost) / (maxCost - minCost)))