To travel from Arusha to Dar es Salaam is easiest by air, however, this will cost about US$200 per person. The cheapest alternative is to travel by bus, which is never advised by tour operators. However, it need not be a nightmare as there are some good companies operating in Tanzania.
The most well known bus company must be the Scandinavia Express. They operate probably the best, safest and most comfortable transport between the two cities; it is, of course, the most expensive private bus option - at US$25 per person - and to book in advance is essential. In Arusha the offices for Scandinavia have moved to Kilembero Market