if and vlookup for excel- help needed

hi...
i am struggling a bit with my spreadsheet task!
so i have 3 worksheet
1- costs- that has all the data in e.g. tables
2- quotation- where the user add the information and workout the total cost
3- breakdown- this is where the quotation (total) cost come from...
i have used if statement to workout the cost per day, discount but it only works for 90 days (user can hire the van from 3 to 90 days) but it won't work if the user wants to hire for 33 days
so i want to just ask for some guidance that how can i use "if and vlookup" statement to make it all work!
i tried this formula but it didn't work
=IF(C4 = "Low" VLOOKUP(Quotation!F13, Costs!$G$5: $H$15,2,FALSE))

To me it seems like it is difficult to help without seeing the spreadsheets, but I don't know, it could be possible to help without them.