Current draw of Receiver and power supply

Hi guys,
My question is quite simple, but I couldn’t find a answer in the documentation, so I post it here:

How much current does APM provide to receivers? Is there even a (hardware? -) limit to this?

Besides, somewhere in the documentation regarding power supply it says that the APM needs over 2 amps of power (I don’t remember the exact value, I think it was 2.25A), which I think is rather much, might this already include receivers? Interestingly, other people on the internet meassured the current draw and say it’s rather around 250mA, which is much more reasonable.

What I want to do is power a RasPi through the receiver port, and basically make a 2g/3g enabled quadcopter (I already had a RasPi and a UMTS-USB-stick anyway), is this possible, provided my BEC provides enough power, or is this a quick way to fry the APM?

Greetings, Luksen