I've donated for a few months at a time back when I was dirt broke. In the short term the extra money can be a lifeline but in the long term it has more health risks associated that I'm comfortable with. There's a lot of conflicting pressures in the actual donor center too. On the one hand they need you to donate at least twice per month to even get enough plasma that it can go to an eligible donor, and they incentivize you coming back as many times per month as is legal; I think it's 8-10 times per month. On the other hand donating that much clearly isn't healthy if you aren't in excellent shape yourself. Do it too much will will make you more anemic and increase your overall fatigue, weakens your immune system, can lead to scarring in your elbows and a fuck ton of other lower chance but more serious complications.
The marks/scarring thing is real. I need regular blood draws and infusions (iron deficiency anemia), and I look like a drug user just because my elbows always have marks, and I'm pretty sure the left one is scarred after I needed a blood transfusion a couple months back.
As somebody who has now needed a blood transfusion, thank you, donors! Please donate if you can. In addition to people needing them for injuries and childbirth, some of our bodies are just shit at making our own blood.
It can vary depending on the area you are in and the demand. I haven't gone in for a few years and am now getting emails with a promotion which would pay out $700 for all the donations in the month. It's a little tempting to be honest. After I get through the first month I think it was about $70 a week with various promotions designed to encourage you to come in twice a week for the whole month.