It's usually not terribly expensive, but difficulty varies between painless and trip-cancelling. Most countries these days will do it online for a nominal fee,

It's usually not terribly expensive, but difficulty varies between painless and trip-cancelling. Most countries these days will do it online for a nominal fee, easy as pie. If you travel around Africa you'll semi-often find yourself sitting in waiting rooms on touchdown for a few hours while nobody can tell you what's going on, but I've never had an actual problem. The only close shave I've had was Egypt, who required me to hand my passport into the embassy, then proceeded to delay for so long that I didn't have my passport the day before my (Sydney-Europe) flight. They wouldn't even give it back without the visa, insisting that they hand it handled. I was only able to get it after going to the embassy and refusing to leave until I had it in hand. Five hours later. But I did get the visa.