I don't know about the others but I recently flew to Pemba and the avgas price was huge. Almost USD 3.50 per litre including VAT. About USD 2.90 excluding. And i thought the fuel in Zambia was expensive. Also they wouldn't take a card from us. Only cash in Mets, Rands, or USD. apparently the price is reflecting a current shortage of avgas due to difficulties in getting it to Pemba? I don't know how true that is though. Maybe try getting hold of CFA as they do a lot of piston engine flying around Mozam.
Cheers,