I was also worried about relocating to Douala.
Here I am now, arrived 3 days ago, and enjoying the city and the people.
The people are very welcoming and helpful.
Like everywhere you have to keep your eyes open and have an ideea about the price to pay in your currency to know if that is expensive or cheap.
Internet is very expensive comparing to Europe, but is available and quick to install (Orange, MTN, Ringo).
Taxi is cheap, it would help to speak French though.
You should avoid saving money to buy electronic gadgets in Cameroon (camera, phone etc. but I guess no surprise here).
I had wonderful grilled fish on the waterside (there is a place with fish restaurants one next to other, alpha-b will tell us the name
) for only 20 euro for 3 people including the beers and suya for 6 euro for 3 persons on "la rue de la joie".
I think soggyboxers says all by: "Life is as expensive or cheap as you want to make it."