Legal Help for a child & family investigator

For the past 10 years I have spent my life behind private accounts and sealed lips do to a physically, emotionally and mentally abusive ex partner.  He is demanding custody of our 6 year old daughter Serenity. 
I have remained quiet and weathered the storm of constant attacks with a smile on my face. Constantly trying to shelter my girls from the negativity. I have never asked for help, though I started to ask for understanding and found it from total strangers. 
Due to his lawyers sending serving my papers to the wrong address ( my address hasn't changed in 3 years) I'm down to the wire to pay for the child and family investigator (CFI) 
My ex partner is fully aware I can not afford a CFI and knows that if I can't afford it the courts will award him custody on default and without prejudice. That will be his first step in eradicating me from her life. 
My children are my world and I would tear down mountains with my hands to let the sun shine on them for another 5 minuets. 
With this CFI I would be able to prove beyond a reasonable doubt 10 years of emotional, physical, verbal and financial abuse that my children and myself have endured.