How do get rid of a lot of black widow spiders?

I live in a 2 story, 4 bedroom home and it is infested with maybe a hundred large black widow spiders mainly in the garage. I have an elderly lady, a baby and 2 cats living here and can't afford to hire an exterminator. Sometimes they come into the house. How can I get rid of them? Very scary and dangerous situation and I'm truly at a loss as to what to do. Please help me with any and all ideas. Thank you so much.