Luckily they gave 3 numbers first, so you avoided a trap many people fall into on both sides of the table - not negotiating at all.
Imagine the first thing a company says after an interview is "what's your number" and you shrug and say "100," and the company reps blink and go "no problem," then pass you an offer. Wouldn't you feel a little skeeved? "I bet I could've gotten more," you'd think. You'd be right. Companies can feel that same feeling.
A bit of back and forth is healthy. It makes both parties feel like they struggled and finally settled on a number that is fair for both (whether or not that number could have been higher or lower). That's why I always recommended bootcamp grads to push back on an initial offer. Always. Worse case the company says "no, this is the limit." Best case, you get more money, the company feels like you were a little bit harder to get and thus more valuable, etc.
I attempted to do research on the company and their salaries for that position via glassdoor, salaries in the area, etc. (they are rated as an open company). They asked what I was looking for in compensation, so I went little bit higher than what my homework said they were paying (this was still substantially more than my current pay), we negotiated a tiny bit on bonuses, but eventually got the amount I was "looking for" in my offer letter.
In the end they ended up being a great company to work for, and I'm really happy there.