It is a different design. The Trends is not SLA or battery powered. I think you are attempting to compare products that at first seems to have the same function, and yet, the execution of the application might be intrinsically different. How Vinnie has told, the main module of the Select is based on the M-Audio device that does not necessarily cost much, and yet, other earlier USB converting devices from Empirical Audio seem to have been based on the same module.
More than calculating what parts costs, what I think you should be looking for is whether the sonics of the product justify what you think something is worth in parts alone.
If you are DIY capable, then perhaps you might be able to approach the idea on a parts cost position, but if that is not the case, perhaps you need to simply ask whether the product in question sounds good.
Products like the Trends are made to give you a certain function, being that I have not heard it, it can certainly sound good, but from many of the reference systems that I have so far heard, NONE used it as part of the digital source. Perhaps some people will call computer audio the David against larger CDP + DAC based systems, but that $100 device does not seem to dent the high end CDP market much.
If you do not want to invest much, perhaps you can use the Trend as a nice experiment, but the need of a separate DAC will quickly escalate the cost of this experiment.
Perhaps you can go check some other people who have computer based front ends.