Hello, Elizabeth and welcome to the forum. Great advice, moral support and pointers on getting started are free
Companies that pay fast, have shops nationwide, and are good starters are MarketForce and Corporate Research International. Grocery shops, if available in your area, can help with the food bills. Some shops that don't require purchases are banks, cell phone shops, some convenience stores, apartments/new homes, car dealerships, mattress stores, and some other retail stores.
Start signing with MSP's who, on JobSlinger, list shops in your area. From there, sign with more - the more the better.
You won't get rich shopping, but it can certainly help increase bank accounts and decrease expenses. Flexibility in accepting work is a plus, though once shops are accepted, they need to be completed as agreed.
Enjoy reading. Mystery shopping is both fun and financially beneficial. Good luck