Hi,
I have a painted Carthaginian force. I will post some images so that you can realize how they can look like (even if I am not a very skilled painter). I have used Old Glory, Essex, Corvus Belli and Xyston miniatures (although I have not painted yet my Xyston ones). My advice is the next one: use as many different manufacturers as you can because you will have a better looking army at the end. You may have problems using some cavalry models from different manufacturers, but that's all. And yes, it is better to expend some more money because at the end it is a better idea.
Here you have an overall look of the army. More or less it is a Carthaginian Starter Army. As you can realize, if you are not an expert you can not notice that they are from different manufacturers.
Here you have a closer view. In my experience you should buy Gauls from Essex, Old Glory and Corvus. The best African Spearmen are from Corvus Belli. Generally skirmishers are cheaper in Essex as you can buy just 8 minis packs (Corvus does not have such a huge variety and I recommend you to use even Greek or Numidian skirmisher for a Carthaginian Army). Gallic cavalry is good in both Essex and Corvus. Spanish cavalry is best in Essex and then in Corvus. The best Elephants are from Old Glory but they come in packs of 4 (so get one pack from OG and the rest from other manufacturers in you want to have six). I hope it would be useful. If you have more questions, just ask us.