Thanks for the replies everyone! I can probably spend $10 per month on this game just for rebirthing purposes. I just didn't know that aside from taking care of your ego/spirit weapon with in-game things, you also have to take care of it using real money
I guess I won't go for an ego/spirit weapon yet since I'm still pretty new anyway and it probably won't be as effective as when I've reached higher skill ranks after taking care of Windmill