If cheaper is important, I'd consider the buy/sell boards and look at whatever comes up. Honestly, all of those are excellent amps that would sound incredible - but they're also, and this is just my opinion, please don't flame - more of an amp than the triple.fi 10s are IEMs. That's not to say they won't make the TF10s sound better - they will.
But if you're going to be spending $500 amp + $150 LOD, or even a $350 amp and a $50 LOD, you could arguably get better overall sound quality by just using the headphone out of the iPhone 3Gs (which is quite good by itself) and invest in a better custom IEM, such as the Westone ES3X.
Here's a review, and the second is the appreciation thread. This would be a huge improvement over the TF10, even without an amp.
http://www.head-fi.org/forums/f103/w...ml#post5432706http://www.head-fi.org/forums/f103/w...thread-409063/