It's tough spending money on any hobby when you're going to (and paying for) school. And saving for a car (for transportation) is more important than spending money on a non-essential hobby. I remember when I first heard the term "discretionary income" and I wondered why I didn't have any of that? Some guys go right from school into marriage and having children, and that can eliminate discretionary funds for years.
If you've got to get involved in pinball now, then you'd better start with as cheap a game as you can find even if it is less than stellar in appearance (as long as its in working order). Once you're out of school and earning money, then there are a number of really good pins that can be bought for reasonable money. Just don't try to collect all the pins in Pinside's top ten until you've found that "discretionary income" that keeps eluding me.