A few years ago, I spent most of my savings on The Lunar Chronicles by Marissa Meyer (Cinder, Scarlet, Cress, Winter, and Stars Above; I didn’t get Fairest), read them all, and loved them…though I didn’t reread them and sold them some time later.
And what was the first series you spent most of your savings on?
I’ve never spent all my money on one series, but the first I got all the books for myself (not as gifts or through my parents when I was a kid) was Full Metal Alchemist. For more traditional books it would have been Spice & Wolf.