/r/gaming, can you recommend me some value games to pick up/your favorite PC games that may be on sale?

tl;dr need recommendations for relatively cheap Windows PC RTS/FPS games, also requests site recommendations to buy cheap games online. I prefer RTS over FPS. Thank you very much for your help!

Hi r/gaming, I've recently discovered the Steam store bundle sales. The value for most of the items is awesome, but unfortunately, the games I was interested in had their sales take place before I discovered it.

I haven't played games in a while, but I have a lot of free time this winter break, and I feel like playing some games. I mostly like RTS/some FPS games; I'm thinking of picking up C&C Red Alert 3 (loved 1 and 2), and possibly the Tiberium Wars; any feedback? Is it worth the $20 to buy off of Origin? A decently active multiplayer community is a bonus, but I prefer single player campaigns. The 1 FPS I have been considering to buy full price is BF3, but I don't really want to dish out the cash for a game I have about a month to play.

Also, does anyone know websites that would sell these games (RA3, BF3, CC:TW) cheap? I would really appreciate it!

Thanks!