My guess it is just the speaker. So whatever specs are on the speaker, a suitable replacement should cure it. But those BA108 are rather inexpensive if I recall, maybe easier to replace the amp on the used market.
As far as am amp for yourself. Are you planning on playing with a band or or just by your lonesome? How loud do you want to get? What is a reasonable budget for you?
I'd look at combos myself. On the less expensive end, look at something like the Fender Rumble 100/200 or even the 500 Combo. Or maybe something in the Ampeg BA range larger than the 108. TC Electronic makes some pretty good ones that have effects too that aren't too expensive.
Have a look in the amp classifieds here and see if anything catches your eye. Used will save some bucks too.