For whole blood, I've only ever been given a t-shirt. For plasma alone though, it was purely dependent on your weight and, therefore, how much they can take from you in the one session. I'm a tiny dude who barely weighed enough to qualify and got about $80 a couple years ago. It's honestly not worth it at all, but if you're broke it's easier than many other options. The place was full of the "undesirables" of society because of that. It drained me emotionally, seeing how blatantly exploitative it is.
Edit to add: these plasma donations can be done with a tighter window between them too, so the people who were always short on cash were in there every 2 weeks.
Edit again: I forgot that that was an introductory deal where they give you an extra $40, so it was actually $40 for me. Overweight patients could get around $70-$80.
Fun fact: Redbox is operated by Chicken Soup for the Soul. I almost got hired by them but they screwed me over after I had already resigned from my previous position.