LPC1788 project modification

We have a project developed on the HOAYU HY-LPC1788 Core development board, and using the MCUExpresso IDE in c . We have some well documented code that needs some modification to add a function, which we believe is well defined. Attached is a sample segment of code in one of the appropriate modules so you can see the degree of documentation.
The added function reads two analogue inputs which are scaled half wave rectified mains signals, looks for the peak value and then multiplies this peak value with a third analogue input which is an input from a current sensor. The current sensor output is shifted so the zero current level is ~1.65v (~1/2 FSD of the DAC). The idea is to look for the direction of power flow (I x V) - if it is positive, we're have a high power threshold before resetting, if however it is negative the threshold is much lower, and the whole system must respond opening some relays within 20mS.
Sampling interval for each of the 3 analogue inputs is of the order of 1mS, and is already in place.
The complete project files and details etc. can be shared on completion of an NDA. Ideally we'd like to work on a fixed price, but realise this is problematic without full documentation and a complete understanding of the system as a whole. If you can give us an estimate of the amount of time you expect to take, that woudl be helpful. We have a limited hardware setup to test the code on - if you are UK based, it may be possible to share the hardware platform for testing purposes.