This is a 19" Rack for 10 api modules. You just have to solder the XLRs to the edge card connectors yourselfs. DIY! ;-)
Edge card connectors are availabel here: http://classicapi.com/catalog/product_info.php?cPath=84_86&products_id=148

The parts shown below will convert the standard NRG CASE 3U into an api rack.

What you need:
1x A NRG CASE 3U
2x Sidepanels (to be able to screw the enclosure into a 19" rack)
1x Rearpanel (for the XLR connectors)

1x Connector panel (to fix the edge card connectors)
2x Mounting bars (to fix the edge card panel to the enclosure, the mounting bars will be placed inside the enclosure)

2x Mounting bars (to fix API modules to the enclosures... the mountings bar will be placed at the front of the enclosure)

 

Side Panels 17,30€/each (you need two)
Sidepanels for the NRG Case to mount the enclosure into a 19" rack.

Rearpanel 57,33€

51x Connectorpanel (this is the panel which is inside the enclosure to fix the edge card conectors) 47,70€ incl. vat

PSU:

You could make an external PSU (and replace the IEC connector with a 5 pin XLR) or you can build an internal PSU.
For the internal psu you will need 2x "sv wmg" from reichelt.de

I can make 3 panels so that you can use meanwell PSU's for +16V / -16V (API500) and +24 / -24 (51X).
If you need 48V phantom you could add an 48V regulator to one of the psu's. Phantompower doesn't need much current, maybe 500mA. You could buy one of the cheap (below 10€) DC-DC stepup converters (3-34V to 4-60V) with LM2577 chip and voltage adjustment. Volker Mayer sells 51X pcbs, as shown on the pictures (yellow pcb).

 
Use these Power Supplies for +16/-16V. It's a 15V Supply, but there is a trimmer so that you can get 16V out of it

MeanWell Power Supply RS-25-15 (Reichelt.de order code: SNT RS 25 15 12,25€)

And use these Power Supplies if you need +24V/-24V:
MeanWell Power Supply RS-25-24 (Reichelt.de order code: SNT RS 25 24 12,25€)

If you need 48V... you could use a stepup voltageconver:
(http://www.ebay.de/itm/3-34V-to-4-60V-LM2577-DC-DC-Converter-Wandler-Konverter-/231156746978?pt=Bauteile&hash=item35d2040ae2)

PSU Frontpanel 16,05€

PSU Sidepanel left 21,20€

PSU Sidepanel right 17,16€

51X/API500 adapter part for PCB 10,02€

(PCB available from classicapi.com)

http://classicapi.com/catalog/product_info.php?cPath=87_88&products_id=401
You can see the yellow pcb on the pictures below, the adapter is to bring the pcb connector to the right position.

Here you can download a layout which interconnects the 4 PSU. You can do this yourselfs simply by using wires.
With this pcb 90° solder pins will connect the pcb with the PSUs.
If you can't etch the pcb yourselfs you could send the pcb layout to a pcb company - for example: platinenbelichter.de

This is an API 500/51X Rack which I'd built out of the NRG CASE.
2 Mounting rails are needed at the front to fix the modules. (the good thing: you can replace the rail. That's not possible if you buy any other rack... if the thread is defective you can't use other racks anymore)
2 Mounting rails are needed to fix the inner panel which holds the edge card connectors.

I used the same PSU which is used for the CAPI Racks.

Make your own PSU by just solderering some wires:
You can also just buy "meanwell" switching PSUs to make your own PSU.
That's easy to do. You just need two PSUs for a positive and negative rail. You'll see that only 15V supplies are available but you need 16V for API... no problem! There is a small trimpot on every PSU which let's you easily change the voltage to 16V.
To get + and - rails just connect the + terminal of the second meanwell PSU to the GND of the first (positive) PSU and you'll have a +/-16V PSU. Same for the 24V. And for the 48V... there are meanwell PSU's available with this voltage.