<human>: Summarize the given text in a few sentences.

Three nights ago when I came home, I found a stray pregnant black cat just hanging out at my doorstep, it has thinning fur on the upper portion of it's back legs. I can't bring it inside as I have 3 cats and it could have any sort of communicable disease. I setup a little bed at the bottom of the basement staircase leading to the laundry room of my apartment using one of my old comforters and a box. She leaves throughout the day and comes back at night time to sleep.

From what I've read, the cat needs a treatment such as Revolution but I can't afford it right now. If anyone can help/give me advice it would be greatly appreciated. I'll be posting pics as soon as she comes back for the night.
<bot>: Stray pregnant cat needs my help, can't bring her it in due to other cats and can't afford treatment, what do I do?