How much will it cost me to get custody of my son?

like i said, he will be 4 in december. i havent seen him since he was 9 months old. i just stopped showing up for visitation. i got sick of the dirty looks from the parents because i used to smoke weed. i already owe income support 20k in child support because my ex turned me in. my ex gf is rehab for meth addiction. i think her parental rights should be taken away. her parents have helped raise the child and now the cyfd placed him with them because they feel that he is safe with them. really? where were they when all the drug use was going on? they claim that she would get angry at them for nagging her to get help and that she would take him and not bring him around. i got served with papers today that they want guardianship of my son, saying that myself and my ex gf are derilects. yeah, i do owe 20k in child support and yes i stopped going around. my parents want me to get custody. how much is this going to cost us? how likely is it that the court will give these people custody of my son? if they do get custody. will i have to pay them child support? i just lost my job and have another as a cook. i do not make a lot of money. i thought parents have more rights than grand parents. wtf? also i want the first court ordered visitation to be reinstated where me and my family can pick him up but the grand parents want me to have supervised at first and go through some parenting classes. i'm not the one that failed to protect him they are! they have a ball bruising lawyer.