eBay, $15 - 20 dollars, tear it apart. Most are SMPS. Your problem is going to be designing and getting the isolated transformer/inductor.
Most people have little or no experience in this area. Even if you did, you have to have one or several made up and that's an issue trying to get them made. Only other real option is to get demo boards from the SMPS chip designers like as mentioned Power Intergrations, TI, National, Intersil, Linear Tech, etc.
Altest if you buy one off of eBay it comes with the transformer/inductor an it works.
Good luck