Omoba is so right. THe prices are going up as we speak - summer is so expensive. They just had some incredible deals on SAA to Dakar a few months ago for the first time. All bets are off for the summer. It will definitely be between $1600-$2000 unless you go through Casablanca and have one of those long and complicated trips to save one or two hundred dollars. I've flown both Delta and SAA, and SAA is absolutely the best, but not always the cheapest. I've used many websites and travel agents, but your friend should definitely try the travel agent that Omoba used and I've had fairly good luck with
www.consolidatorwebfares.com.
The rainy season will really kick in in Dakar in August. It's pretty hot (don't know what you friend is used to) in July/August, but I personally don't ever think Dakar is too hot. If you are going inland, yes, it's hot. I think foreigners are given a lot of latitude in terms of dress, but I have never found it respectful or felt comfortable wearing anything short. When people go to the clubs at night, it's another story, but in the daytime, people appreciate it if you cover your legs and respect their customs. If someone is doing research in the country, that's even more important. No one will do anything to you though. There's, no need to cover your arms. It's a very moderate country.
Dakar is a very cosmopolitan city and there are cybercafes everwhere. The prices will differ depending upon what part of the city you are in, but you'll pay an average of a dollar per hour for internet access. Printing is expensive. Some hotels have internet access either through cable or wireless for their customers. All this can be googled though...good luck!