i think the fireball is more similar to a 2-channel savage than powerball.
Basically, the fireball has two channels: clean and out-and-out br00tal death metalz gain. I wouldn't buy one unless i was a 100% modern metalhead.
Screamer is a lot more versatile, having 4 channels. Can do everything from clean to metal, but if you only play metal, the fireball will do that better, it has more gain, more low end, etc.. But if you need much (or indeed any!) versatility, the fireball is basically a non-starter.
The blackmore would be another suggestion in that (rough) price range. it's my favourite of the "cheaper" engls. Will do metal and hard rock better than a screamer, in my opinion, while remaining a lot more versatile than the fireball.