I have a MS in environmental engineering. (I considered getting a PhD but decided not to simply because I knew I eventually wanted to be a stay at home mom and figured I'd be better off getting a job and paying off debt from undergrad.) I was able to get a research assistantship position that paid me a small stipend (it was enough to live off) AND provided health insurance (I got the same insurance as the faculty), so I would definitely recommend looking into universities that are more likely to provide you with that kind of funding. I got a book from my undergrad advisor that listed stats such as % of students that get funding. There are also several different outside funding you may be able to get. Several people I went to school with got funding from the National Science Foundation and the EPA. Also, you are more likely to get funding if you are going for a PhD.
As far as my experience, I found it easier than undergrad. I LOVED grad school! I took 1-3 classes a semester and the rest of my time was spent working in the lab, and I was able to do that mostly on my schedule. The people I met were awesome and I had a very active social life <img src="i/expressions/face-icon-small-smile.gif" border="0"> Everyone knew I had CF and it was no biggie (although I didn't make a point to share that info before I was accepted). I remember nebbing at football parties. I also used to sometimes wear workout clothes to the lab, start and experiment, go for a run, and then come back to the lab and finish it up all sweaty.
I would also recommend visiting the school and talking to the current students so you can get an idea of the vibe there. I went to a very good school and loved it, and when I visited the school, I could tell that the students loved it. I have a friend who went to s t a n f o r d and she hated it because the students were not friendly and very competitive, and it was a ton of work. She got a ME, though, and not an MS, so that is a difference.
IMO, if you did well in undergrad, I think grad school will be just fine!