Not sure exactly how much at the moment.
I have done a few changes, as well as bought a few qts since last full inventory.
Off the top of my head I know I have:
~5 gallons of Peak 15w-50 (~$0.50/qt).
~25 qts of Castrol Magnatec xw-20 ($0.05/qt)
6 qts Castrol Magnatec 10w-30 (~$0.85/qt)
2 qts Valvoline Conventional 30wt ($0.05/qt)
15 qts Pennzoil Platinum/PPHM 0w-20 (Free, may have paid me after rebates)
10 or 15 qts Valvoline Synpower (5w-20 and 5w-30)(~$1.75/qt)
5 qts Mobil 1 EP 5w-20 ($2/qt)
~8 qts Castrol GTX HM 5w-20 (~$0.25/qt)
2 qts Pennzoil Platinum (Free)
2 qts Autozone Synthetic ($2.65/qt)
Maybe some more?
Here is the most recent pic I have from a few months ago.
15w-40 is for bike.
xw-20's are for my truck (6 qts/change, + 1 qt make up every 1500 miles), wife's car (4 qts), brother in laws truck (7 qts/change + 1 qt make up every 3000 miles) and sisters SUV (5 qts/change + 1 qt top off every 4000 miles)
xw-30 is for my mom's Saturn (5 qts)
I bought the 30wt for my lawnmower, but have since gone to an electric mower (will probably use it as top off oil)
this is a good 3 years worth of oil (if I don't buy any more).