Don't try to have any US company make it for you, that is just asking for trouble if you are not a legitimate business.
What kind of batch sizes does a typical custom synth co. require one to buy? what do they consider a small batch?
They don't require anything, usually. But as their initial costs for a new compound are much higher than the actual costs for chemicals etc, they may charge you $500 for one gram, but only $2500 for 100 grams (I have no idea about the actual costs for 2C-I, I'm just trying to illustrate that you may need to order a certain amount for their fee to be cost-effective for you, as they couldn't care less about that - they simply charge you for their time and expenses).
It is hard to say what is a small batch or not, for a simple substituted benzaldehyde, orders below one kg would probably be small, but for a complicated biomolecule with several stereocenters, orders of more than a gram might be considered a lot.
Also, the easier it is for them to figure out a working synthesis of the target compound from commercially available precursors, the cheaper it will be for you. If you can supply them with a journal article which details a high-yielding cheap route to your desired compound (in as few steps as possible, their chemist's time is expensive), then your final cost per gram will be considerably less than if you just give them a target compound with no clues for them how to make it. If there are no reported syntheses of the compound in the literature, then it can become very expensive, as they may need to experiment a lot first before finding an optimal synthesis.