If I understand your question correctly, this well beyond the scope of this forum. Designing electronic circuits that convert wall socket voltages (120/240AC) to a DC voltage/current required to charge batteries requires very specific skills limited to a niche electronic engineer called "Power Supply Designer". These type of electronic circuits are not for the naive or uninitiated, incorrect design can be lethal. To that end, any electronic circuit designed for this application must be UL compliant (in the USA) so that it is certified not to be life threatening.

Having said all of that, $250 retail pricing is a very aggressive target for the power level required for reasonable battery charging time. As a first pass, I would take a look at an off-the-shelf solution from an Asian internet vender just to see what kind of ball park you're in wrt pricing.