First - bless you for rescuing these guys. I love to see abandoned animals find love and affection and a permanent home.
I would start with something simple to begin with. I would assume that these guys probably have fleas and the incessent scratching is what is leading to the hairloss and skin problems.
I would invest in 2 products - Capstar which will give them immediate relief from the biting within an hour and then also a proven/safe monthly topical treatment. I would suggest either Frontline, Advantage or Revolution (no revolution if the dogs are collies or collie mixes). Once you have treated with the Capstar orally, then treat with the other and they should be good for 30 days.
If neither of these help, then your vet is going to have to do a skin scraping to see if they have mange or some other parasite causing this. Below is a list of organizations that can help people who are having financial problems and are unable to vet their animals.
American Animal Hospital Association
" Through the AAHA Helping Pets Fund, veterinary care is possible for sick or injured pets even if they have been abandoned or if their owner is experiencing financial hardship."
Angels 4 Animals
"Our services range from financial aid to complete treatment
to those pets and pet owners in need."
A credit card company for health care, including veterinary care.
"With a comprehensive range of plan options, for
treatment or procedure fees from $1 to over $25,000, we offer a plan
and a low monthly payment to fit comfortably into almost every
God's Creatures Ministry
"This fund helps pay for veterinarian bills for those who need help."
"Our efforts focus on serving the elderly, the disabled, and the
"We are dedicated to insure that no
companion animal has to be euthanized simply because their caretaker
is financially challenged."
The Pet Fund
"The Pet Fund is a registered 501(c)3 nonprofit association that
provides financial assistance to owners of domestic animals who need
urgent veterinary care."
United Animal Nations
"The mission of LifeLine is to help homeless or recently rescued
animals suffering from life-threatening conditions that require
specific and immediate emergency veterinary care. We strive to serve
Good Samaritans and rescue groups who take in sick or injured
animals. In certain cases, LifeLine can also assist senior citizens
and low-income families pay for immediate emergency veterinary care."
They also keep a list of local and national help resources here
Good luck and let me know if I can help further!!!!