I spend as much of my time on safari as I can, ex our second home in South Africa, with my A900 and my Dynax 7D. My lenses are all Minolta G - a 300 F4; a 200 F2.8; and an 80 - 200 F2.8. I also use a Sony and a Sigma 1.4 TC with the first two and sometimes a Kenko Pro 1.4TC with the zoom. All the G lenses came from EBay in UK at prices between £300 and £850.
My experiences : the zoom is great for the larger animals that are fairly near but much of the action is invariably a fair distance off so the 300 with the 1.4TC (ie 420 equivalent) is usually the best option. Quality wise I do not find the 80 - 200 as good as the fixed length lenses (but I am a being very critical). The 200 with the Sony 1.4 teleconverter is actually just as good as the 300 without (and much smaller and lighter). But my preference is to have the 80 -200 on the Dynax 7D and the 300 with the Sony TC on the A900.
You also need to factor into the mix that most of your game viewing will be done on early morning or late afternoon game drives. In the middle of the day everything is sleeping or hiding. So light will be an issue in the first hour or so in the morning and the last hour or so in late afternoon. So an F2.8 will be better than an F4 although it is sometimes better to trade film speed for a higher aperture and a better depth of field.
NB it is often very dusty in the African bush and you should definitely try to avoid changing lenses whilst out on drives. If you have to, use a plastic carrier bag. For this reason, although it might not be the right thing to admit on this forum, I therefore use my little Sony W220 a lot for scenery or wider angle shots.
Also remember when photographing anything fairly close to turn the autofocus off. For some strange reason the autofocus noise seems to either get animals to shoot off fast or, in the case of elephants to result in the exact opposite - i.e. a rapid charge...(and the drop camera, start engine, reverse fast, sequence of action...).
As others say, always go for a G lens rather than the alternatives; purpose of my post is to say also look at secondhand Minolta G lenses. They will last you a lifetime.