My developer got the function to work well changing just a few code lines in one file only!
The way we made it is like: everytime a new project is posted in a category, all freelancers that subscribed in that category will receive an automatic invite, as if the user had invited all freelancers to bid in the project… I used AE Fields to create a new field for Categories of Interest and freelancers can subscribe to them in addition to the original one the theme permits.
If you want the feature we can share its costs, I payed in reais but convertng to dollar it would be 83 dollars. if you want we can share it at 40, via paypal?
its one file you`ll have to change and one word that probably is different from mine, but all in this code of the same file.