Actually pedigreed kittens START at around $600 for pet quality.
You don't "buy" shelter animals you ADOPT them. Most shelters charge around $100-$150 for kittens and most charge a lot less for adult cats.
These cats/kittens are altered, shots, disease tested, deflead, dewormed, microchipped. All of that costs the shelter at LEAST $400 PER ANIMAL. Many animals also need additional vet care - like the senior Himalayan I adopted last year with FOURTEEN PAGES of vet records of things they had to do to save her.
There's also the cost of feeding the cats and kittens, litter, litter boxes, toys, beds. Rent or mortgage for the facility. Utilities. Insurance. Paid employees. Maintenance. Licenses. It's VERY expensive to run a shelter.
If you get a "free" kitten or cat from someone odds are it will have little or more likely NONE of the things a shelter's vet does to the animal so you're looking at $400+ out of pocket for those vet bills.
So you REALLY think $150 is a "lot"???