So then, why don't you create a spreadsheet where you've got all the months and calculate the cost for the missing months in there? Would that not be much easier?
If you don't want to do that for some reason, then I'll have to create a loading process in Power Query for you. Can you please share the spreadsheet via a link to OneDrive, Dropbox or Google Drive? I don't want to create it myself as I'm at work right now and busy... Thanks.