I searched and searched for DD's calculator. I was determined to get the one that the school recommended for the best possible price. I ended up finding a sale at Staples (think it was $99) . . . and price matching it to Office Max, where I had a $15 or $20 off a $100 purchase card (can't remember exactly how much the coupon was for -- and I had to add in some pens or something to pass the $100 mark) . . . and then I used my teacher card, which gives me a rebate every quarter. I don't know how much of the rebate I received came from the calculator and how much came from other items I'd bought, but I was satisifed with the cost. It ended up being better than I could do on ebay, and I knew it was brand-new.
I did think it was worthwhile to buy "the calculator". The teachers have a special calculator that hooks to their overhead projector and projects the work, and they demonstrate how to work problems on THAT CALCULATOR. I thought having the exact model that the teacher uses would make life a little easier.
Also, my math teacher friend told me that the TI-84 Silver Edition Plus (the current "it calculator") should see her through both high school and college. I didn't mind buying an expensive item . . . but I didn't want to buy a $50 calculator this year and then be forced to buy a $100 model two years later. I wanted to make the purchase JUST ONCE. She also understands that IF it gets lost or stolen, it will be replaced with a $1 four-function calculator.