Vlookup that sums multiple worksheets based on two criteria

I need to create a formula based on two criteria. I need it to look at each sheet tab's data and pull in the cumulative total.

There are currently 26 sheet tabs that may contain the criteria. There are three columns on each sheet tab. The criteria will be based on the first two columns. The third column contains the cost. I just want to add the cost wherever the criteria matches.

Please no VBA programming.

Thanks in advance for your assistance!