I have had my Aurora Dual Power Calculator for years, and it still works fine. I purchased it for about $15.00, but I know you can get it for much cheaper online now.
This is a dual power calculator. It works by solar power as well as an internal battery. The buttons are a nice size and easy to press, which I like because I don't have to use my fingernail to hit the button. My husband likes this feature because he has bigger hands and finds this calculator easy to operate. The numbers are also big and easy to read. The Aurora calculator has a long answer bar across the bottom, as well as all of the other standard buttons.
This calculator is also very durable. I've dropped it several times, once it even caused the readout window to loosen somewhat, and still the calculator functions fine. In the time that I have had it, I have never had to replace anything. The size is also a nice feature, 6" long x 4" wide.
If you are looking for a reliable calculator that will give you good service and will last a long time, I would recommend the Aurora Dual Power Calculator, Model DT150M.