(In my spreadsheet, Category is column D, Price is column E).

Category Price Paid?
Core $55.50 yes
ESL $20.00 yes

Conditional Sum Formula for "Core":
=SUM(IF($D$2:$D$52="Core",$E$2:$E$52,0))
Conditional Sum Formula for
"ESL":=SUM(IF($D$2:$D$52="ESL",$E$2:$E$52,0))
The ESL one works fine; the Core one doesn't!!