Unless OP is going to setup his own darkroom at home, I wouldn't "invest" in one....

Most commonly used ones today are made by Ilford and they are not that expensive.
http://www.adorama.com/searchsite/de...&category=1184

Depending on size and location, they range from 27 dollars to 70 dollars.

Scratches here and there doesn't actually degrade images visibly. Unless you really want one of your own, I'd just use the one the school has....