As of early December 2014, a visa on arrival at Bole International Airport costs US$50 (or the pound or euro equivalent). This US$50 visa is valid for 30 days, which was the maximum period that the immigration authorities would stamp in your passport when I passed through Bole in early November 2014.
We have heard that a three-month visa now costs US$70 but it is not clear whether this type of visa is once again available upon arrival (as it was until at least as recently as July 2014, when I had one stamped in my passport at Bole) or must be bought in advance. If anybody passing through Bole feels like checking this out, please let me know and I’ll post it here.
Note also that the fee for an annually renewable resident’s ID card has also risen from from ETB 400 to ETB 1500