Hi
I have been working with Joomla for quite sometime (over 8 years) and have had our own component stream as well. We would be more than happy to work on this project and do the relevant customisations.
As you mentioned, there might be minor modifications along the way, we might be even be able to capture these within the budget (i.e. without increasing), but of course, let's talk and see :)
Hope to hear back from you,
Have a great day!