Trying to sum up textual grades into total sum to be paid

So bassicaly what i'm trying to do is, i have my scorecards and employee grades up (the tables are relatively large and are divided into weeks and hence, different sheets). What i'm trying to do now is to populate a new table with all the grades for 4 weeks and i've managed that using VLOOKUP, and lastly sum it all up. The problem is the grades are textual (Fantastic plus, fantastic,...) and i want to find a way to assign a numerical value to those textual grades that will allow me to sum it up into a "to-be-paid" ammount. Any help or advice is appreciated.