Tiered Commission - Flat Rate

Hi all,

After searching and searching, figured I'd try asking the question -

I'm looking for a way to calculate flat commission (not percentage) based on tier levels. Here's an example:

TIER 1: 1-4 Units Sold = $25 per unit
TIER 2: 5-8 Units Sold = $42 per unit
TIER 3: 9-15 Units Sold = $103 per unit
TIER 4: 16+ Units Sold = $123 per unit

I'm currently learning Excel, so I blame it solely on my lack of knowledge at the moment. The problem that I run into is that I need TIER 1 to STAY at $25 per unit, TIER 2 to STAY at $42 per unit, etc.
example:
4 units sold = $100
5 units sold = $142 ..and so on
Right now, my calculations cause 5 units to ALL jump to $42 making the result $210

All my searches bring me around to percentage calculations and I have yet to find a formula that does what I need it to. I've worked in Nested IF and even tried SUMPRODUCT but haven't been able to return a successful calculation. Any help is appreciated as is your patience in a "newbie" like me.

-RJ

Thank you shg!! - and for getting back to me so quickly!