Oh boy border crossings in Africa are difficult. Long trips from one country to another are exhausting and Dar Es Salaam to Malawi is no different. There is no easy and cheap way. You can fly but that would leave you $300 short.
I’ve read many different options that people used to travel this route but here is what conclusion I came to.
Taqwa bus Dar to Mbeya leaving Kariakoo 4am or Ubungo terminal at 6am sharp and arriving to Kasumulu border around 2am next day. 40,000Tsh ($18/£14)
You can stay on the bus and sleep or get a room for 20,000Tsh ($9). We stayed on a bus.
Border opens at 8am. Exchange money on Tanzania side, as rates are incredibly good. Get passport stamped to leave the country and walk to Malawi immigration. Visa cost $75 and they take only US dollars, so make sure you have that sorted.
Then get a free ride to Karonga. I ended up chatting with a guy going that way with his car.
From Karonga take a bus wherever you’re planning on going. I went to Mzuzu in order to reach Nkhata Bay. If you going same way use big bus and not mini bus, it’s cheaper and more comfortable (3000Mwk/$4/£3).
From Mzuzu get minibus to Nkhata Bay, they’re leaving often and cost 1500Mwk ($2).
Whole trip cost $24, which is pretty cheap considering the distance.
Whole trip took about 35hours but as I said there is no easy way to do it for cheap.
Update: many bloggers mentioned Scandinavia buses that are quite luxury, however they’re not operating anymore. You can buy Taqwa tickets in their office in town. Or can always ring them on +255716031819.
Hopefully this information is helpful as when I did research there was a great struggle to find a straight answe