Your mac has garage band on it which should be more than enough for what you're trying to do.
If quality is your concern, focus on getting your recording space acoustically treated as much as possible.
At a bare minimum, get yourself a reflexion filter, or a kaotica eyeball.
Ideally you want the entire room to be acoustically treated but many people can't due to space restrictions.
I can't stress enough how important getting the right recording environment is.
Don't bother looking at any new equipment until you get that in the best possible condition.
Next I would look into getting a decent microphone and preamp.
If you want, you can share your budget and current set up and I can help push you in the right direction so you don't go spending money on the wrong stuff like I did when I first started.
Here's some pictures of my current set up at home.
Finally finished my recording studio