You may find calculators be very useful when you need to work on basic or repetitive mathematical calculations. However, it may be difficult for persons with low vision or learning disability to use calculators independently.
If you are looking for a calculator with additional arithmetic features for persons with low vision and learning disability, this Double Check Talking Financial calculator can be helpful.

The features include: calculate percentages, extract square roots, raise a number to a given power or identify the reciprocal calculations. It also offers conversion features and use different preset factors in calculating volumes, length, weight, temperature or currencies.
The Double Check financial calculator has a reminder feature and alarms. It has big and clearly arranged keys with 10-digit-display and clear and natural speech output. The results can be announced by either be as a total number or digit by digit. Earphone jack is available so that you can use a headset. The price ($99) is expensive compared to a basic talking calculator, but it is far less than other advanced calculators.
If you have a student with low vision in classroom and need to have a calculator with scientific, statistical, and trigonometric functions, Low Vision Talking Scientific Calculator and TI Orion TI-34 may be helpful, but these advanced scientific talking calculators cost $459 – $650.

If you do not need special features and only need a talking calculator on basic calculations such as addition, subtraction, multiplication and division, you can find these basic calculators around $10 – $20.
Some of the basic calculators are:

LS&S Talking Calculator, Reizen 12-Digit Jumbo Talking Calculator, Desk-Top Talking Calculator