Get the COD collection 50% off for 200$ haha

I check in on steam sales every week. I suggest you do the same, you can open all sales in a list and sort by reviews.
Steam also selects interesting titles for you based on what you already have in your library.
But yeh, go for the 75-90% sales. You can try out a lot of nice games for near free.
And ae, there's a lot of free-to-play stuff in the weekends lately, as well as games that are always free to play (but usually stimulate u to invest money in it to get further in the game).
edit: and GTA5 on PC is supposed to be awesome, with a lot better graphs than on console.