Steam key of collection is $15
Green Man Gaming has a slew of Tomb Raider titles on sale, from the classics to the latest Lara Croft and the Temple of Osiris (only $7.70 after coupon).
Tomb Raider Collection, which includes basically everything except Temple of Osiris, compiles 11 Tomb Raider titles and most of the related DLC. You can also grab any of the games piecemeal.
Everything listed below is a Steam key.