We prefer not to use any prophylaxis against malaria (take the usual precoutions, carry a test kit and emergency solution in case you do end up getting malaria), but sometimes that isn't the wisest things to do...
In Southern and Eastern Africa they will sell you Doxycycline
as a prophylaxis against malaria and this is quite cheap (compared to buying prophylaxis in Europe).
Recall 7 euro / 10 USD for about 100 pills. With one pill a day, this will give you roughly 3 months... I wouldn't use it any longer than that, to be honest.
This stuff seems to work against almost everything, that can't be healthy
PS: we found those Malaria test kits available at the better pharmacies in Southern Africa for about 10 euro a kit