1- Use a formula like: =SUMPRODUCT(NOT(ISERROR(FIND(C794;$C$2:$C$789)));$D$2:$D$789), FIND() function does not use regular expressions.
2- Using SUBSTITUTE() function to replace in the second parameter of SUMIF() the parenthesis for \parenthesis ( -> \), but are needed at least a couple of SUBSTITUTE() nested, one for open and one for close parenthesis. =SUMIF($C$2:$C$789;SUBSTITUTE(SUBSTITUTE(C794;"(";"$$");")";"$$");$D$2:$D$789)