It's not just homeless people. Every floor of the parking garage in our building used to have a shopping cart (thank you, QFC), until someone stole them all. Those things were really useful! Every time we got Costco-amount of food, we could use a cart to get it all upstairs. Now that carts are all gone, the residents are kind of pissed.
Shopping carts are relatively expensive. Metal ones (cheap steel covered in chrome) are $1000-2000 each. Plastic ones are probably about 10%-20% cheaper.
According to Wikipedia (I know, not always the best source), the average shopping cart is under $200 and can go as high as $400 in some places). Not sure where you're getting the $1,000 to $2,000 figure.