At least in the US you can regularly find fully free or super discounted spay/neuter services through various charities. Don't know about other countries, but generally speaking price should not be an issue for this.

Don't put it off to do later as they will multiply. Cats don't give a singular shit about incest.

Like it or not, whether they are fully outdoor feral or not, you are feeding this cat and it does see you as part of its pack. That's exactly why it brought you the baby to show you, and you clearly know it.

I grew up in a house where my parents did not take spaying/neutering seriously until they had already gotten an explosion of two (or three? I tried to stay away from home and have blocked some out) litters of kittens.

I love cats. It was awful, and there were too many cats to try and properly care for any of them. Litterbox training? My parents were too busy/lazy to do it properly. Augh.

I'm really trying to be strong about this but I think I have some actual unresolved trauma about it. Don't let this become a problem because you won't accept responsibility for it. Doing the bare minimum here is easier than you'd think and immeasurably worth the trouble.