Can't think of anything off the top of my head. I've heard that Beez custom services are pretty user friendly.

I'd say that any slick, tight-fitting carrier would foot the bill - especially if the carrier is made to carry a standardized plate size.  The stretchy material in the plate pocket of the Crye JPC would probably hold backers well without sagging.  But youll need to scour the used market to stay in budget.  The SKD Brigandine might also be perfect if your backers are truly ESAPI shaped.  

In your situation, I would use them as backers for rifle plates or sell them to fund something else.

If you want a police/concealable type vest, don't waste any more energy trying to re-invent the wheel, and just go buy that style of vest.