Often you can replace nested IFs with a simpler LOOKUP type structure, or in this case, INDEX/MATCH. E.g. in place of this part of your formula

=IF(Inputs!$B$8>=75 000,Inputs!$B$8*Inputs!$E79,IF(Inputs!$B$8>=50000, Inputs!$B$8*Inputs!$D79,IF(Inputs!$B$8>=15000,Inputs!$B$8*$C79,Inputs!$B$8*Inputs!$B79)))

you could use

=INDEX(Inputs!$C79:$E79,MATCH(Inputs!$B$8,{15000, 50000,75000}))*Inputs!$B$8