I am trying to set up an incentive matrix for sales reps. If there were only
3 clearly defined tiers or payout %, then I could wrap this up with an IF
formula. What I actually need, however, is some way of calculating infinite
ranges in between my established tiers. So let's say my sales reps have a
goal of selling 100 widgets per month at a cost of $1000 each. My tiers are
constructed like this:

% of Goal Achieved % of Revenue Share
Tier 1 90.00% 0.75%
Tier 2 125.00% 3.00%
Tier 3 150.00% 4.50%

If, for example, the rep sales only 89 widgets, he gets no revenue share.
If he sales 90 he gets 0.75% of the revenue (in this example that would be
0.75% of $90,000 or $675). But if he hits something like 107.5% of his
widget goal, then I want it to calculate a percentage of revenue share in
between the first tier (0.75%) and the second tier (3.00%). And then I need
the same sort of calculation to take place if the numbers lie in between the
2nd and 3rd tiers. And of course I need it capped at 150% of goal...so the
most the rep could ever make is 4.50% of the revenue.