After decrypting an IPA file on a jailbroken iDevice, you can use a much more affordable alternative to IDA Pro called Hopper - the multmulti-platform disassembler for < $100.
http://www.hopperapp.com/https://www.hopperapp.com/
It has support for analyzing iOS executables (among others) and even comes with the ability to convert ARM assembly to pseudo-C.