Hi there, I'm betting it's possible with a calculated field (probably the number or currency field format is what you need). You could have the answer from your project custom form field automatically appear in tasks with your task custom form that call that project form field. Then you should be able to add the presence of an answer in this field in a task report (by custom form field name > is not blank).
I've done this with a program custom form field that I wanted to show the answer to in projects with a certain custom form and my calculated field looks like this:
{programMM|program}.{DE:What category does this Program fall under?}
The DE/custom form field is my program form field. Happy to show you this on a call and see what we can figure out : )