The local currency is Tanzanian shilling, which current exchange rate is 2175 shilling per 1 USD (mid-rate).
This currency is easy and safe to get in any ATM. There are several of them in all the big towns, but if you are travelling out of town, make sure you have enough Tanzanian shilling for your own needs, and make sure you know when the next chance to see an ATM is. Even exchanging money is very expensive most places far from town.
USD is mainly used in the business of tourism. When you are traveling with Paka Adventures you do not need to worry about this, because all your expenses will probably be pre paid.
You only need your 50 USD (100 USD for Americans and Irish) for the VISA, but other than that all food, tip, and souvenir shopping are calculated in local currency. You can, many places, pay with dollar, but that is always giving you a bad rate.
Bureau de Change is located in all big towns and will usually give you a fair rate, but be careful not to get fake dollars.
Traveler’s checks – simple advice – do not bring them! They are very difficult to use.