I have no way to calculate over 20 years of gaming purchases. I have own stuff from the Atari era through today. I would have to catalog so much stuff it would take days. Plus there's all the related media like books, artwork, soundtracks, collectables, etc. I've imported games and consoles, bought used and new stuff. There's bargain bin goodies, and DLC stuff. I've built three arcade machines, several computers, shelving, and custom joysticks. I didn't keep receipts so I'd have to try to remember what it all cost or estimate it.
I should catalog, photograph, and record it all for insurance purposes. Stuff like my Panzer Dragoon collection and Working Designs stuff has gotten very rare and worth far more than when I bought them. But like I said it would take so much time I'd lose at least a weekend going though it all.
