QB owns over 90% of the market for small business accounting. Thus if you need help its easy to find and/or its easy for the next person to take over the QB from you. I would not buy the non-profit verision, just buy the basic package.
If you don't want to pay for QB I think you're pretty much left with excel. I imagine their isn't a whole lot to account for a High School team so excel maybe the way to go. Just do a spreadsheet to keep a runing balance of the bank account and add columns to summerize data as you desire.
btw you can use a single copy of QBs for more then one company at a time, so if you already have some verision of QB, other then on-line, you don't need to buy anything, you already have it.