75? The last project I did was my L6 and Maverick taking both from G3 to G5 when the Revenants turned up. I don't think it required 75 MI but I did have quite a few in my inventory and Carrier.
You need 10 MI to get from G3 to G4 and 15 to get from G4 to G5 - and i was nice enough to assume people went through the random Thursday shuffle to find their G3 pre-upgraded stuff. So only 25 MI for a single G3>G5 upgrade
1 suit and 2 weapons - there is goes. 75 MI.
So while i may have a number of mats stashed away - they may get burned really fast
My preferred source of MI is still running missions for allied factions and negotiating 10 MI for a mission (that hopefully i wont fail

Rest of my materials mostly come from power restore missions, using an increased backpack mav, taking everything that is not bolted on, then trading at the bar for the expensive stuff... but data still kills me.