Final piece to my family puzzle. Help with my DNA cost please

I have always known I was adopted so the thought of one day meeting my birth parents was there early on in my life.

Growing up an only child with some health issues I struggled at times to fit in.

In 1993 I became a father for the first time which created the start of my search for answers.

Recently that has become a grandfather.

This search was not easy in the pre Internet days and it wasn't until 2002 when I made a random connection with a person in England who turned out to be my maternal Aunt. She put me in touch with a local uncle whom I have met although that he denied me knowing where my mother was due to her mental abilities.

None of my "family" knew I existed based on the fact that my mother was exchanged for fruit and veges while my uncle picked the food while waiting.

My mother become pregnant at 15 to the person I suspect is my father (Charles) when he was around 47 however due to my eldest Aunt blowing the whistle on what was going on I was born in State care and then fostered/adopted out.

My birth mother came out of Kingseat and then married Charles in 1975 going on to have 2 children.

Due to her mental abilities she is difficult to get any memory from only vaguely remembering the two children she was married to Charles.

Charles died in 1981.

Charles died of colon cancer which was diagnosed around 1969 ish (he would have been about 44 where I am 44 this year) based on his death cert as well as a secondary spread a couple of years from his death in 1981.

For medical, historical and emotional reasons I am desperate to either prove or disprove that Charles is my father so that I can then apply for more records and details including the possibility we have another older sister.

I am trying to raise the $699 to do a sibling test. Please even the odd dollar here and there will help. Thank you