The thing about customs is that you have to be sure about the sound signature because you can't sell them if you don't like them. The cost of the impressions is not recoverable, and there is the hassle factor and wait time. I've had multiple impressions for 2 pairs of customs, so I have some experience in this regard.
No matter how much you spend on customs, they will not have the soundstage of full-sized headphones, and if you check the threads for various custom IEMs, there are complaints about fit and performance of customs as well.
I would say that if you have no problems with fit and isolation with universal IEMs, then the advantage of customs is not that huge, especially if you find a IEM with a sound signature and performance you like. If you have a universal you don't like, you can sell it. If you love that sound, you can add custom tips later.
Otherwise, think of customs as just another portable solution with unique audio characteristics. They don't automagically sound better by virtue of being customs, nor does everybody find them comfortable. If the impressions aren't done correctly, you will certainly be dissatisfied with the IEM. There may be some tweaking and new ear impressions involved.
That being said, if your budget is around $350, I have experience with Livewires. The LW is a quality IEM, and performs better than many universal IEMs I've tried at around the same price. There is crystal-clear detail, a slightly analytical midrange and great bass extension and detail.
If you're looking for a warm liquid midrange, or a subwoofer-like bass, the LW is not it. If you're looking for something analytical the scales nicely with your portable components and reveals subtle details, it is hard to beat the LW at that price.
If you're not in a hurry, check with Ultimate Ears or Livewires and see if you can audition one of their 'universal' customs - basically it's their custom IEM with a nozzle that will fit a foam or silicon tip. It will give you an idea of what that particular custom sounds like. CanJam 09 is probably a good place to check this out.