Design of a low cost/low power Isolated AC/DC SMPS
You won't be able to make this low qty/yr cheaper than buying direct.  

The cost of failure exceeds the savings unless you have done this before.  But choosing a transformer 1st tells me otherwise. You always start with detailed specs.

You still have to select many sources and perform DVT to their specs and your requirements with accelerated stress tests.  This is probably what you omitted last time.


You cannot expect $0.1/W prices in a 2.5W supply. 
You ought to budget 1 month of work doing Design Verification Tests (DVT) with at least 10 units from each supplier.  
This should include a teardown reverse-engineering analysis. If you know how to design, then do this.  This is essential for high volume users who rely on high quality from the cheapest sources. 


Best quality comes from Japanese parent companies like  TDK, OKI, etc.

This looks like the best CUI model distributed by DK. $4.43 @ 540 = qty. They do not make them but are custom made for them under their US brand.