I was in Zanzibar (Stone Town, Nungwi, Paje) in late December 2019.

Here are some random thoughts on renting a car:

1.The driving there, both in Stone Town and on the roads and highways, seemed pretty civilized.

2.From what I remember, the situation with road and street signs was not great. I would not
rent a car there unless I had a cell phone with data for directions and maps. Depending on
where you are going in Stone Town for your Covid test, it could be tricky due to the lack of street
signs, narrow one-way streets in some cases and difficulty finding a secure place to park.

3.I have not driven the exact route that you will be taking. It might be fine. However, I can tell you
that driving from Paje in the southeast to Nungwi in the north, in the center of the island many
of the roads were unpaved and had enormous potholes (large enough to wreck the car if you
came upon one at night and did not see it in advance).

4.I would avoid driving at night due to the aforementioned potholes as well as people walking without
torches and animals on the road.

5.Considering the distances involved (Airport to Mangapwani 29 km, Mangapwani to Stone Town 23 km)
I don't think that the cost of petrol is going to be a major expense.

The taxi prices you mentioned seem quite high to me. As I recall, we paid about $35 one-way for a taxi from
Nungwi (which is about twice a far from the airport as Mangapwani) to the airport. According to the web site
rome2rio, a taxi from the airport to Mangapwani runs $16 - $20 one-way and a taxi from Mangapwani to Stone
Town runs around $13 - $17 one-way. I am no expert, but these amounts seem about correct from my
experience (although you might have to bargain and shop around to get them).

If I were in your situation and planned to spend all of my time at the resort, with only the brief trip into Stone
Town for the Covid test, I would probably just skip the rent car and use taxis. It will definitely be less stressful
and likely end up costing less than the car rental plus the $10 for the driver's license plus the cost of petrol.