This post is not going to try to convince you to homeschool. However, if you are interested in learning about it, email me and I'll be happy to give you any info I have. Anyway, this post is about spending wretched amounts of money on homeschooling.
There are too many types of curriculums to list, but I will say that the 'all-in-one' packages can easily be $1000 per student per grade level. The only time I would recommend one of those is in the case of Missionaries, who are going to be overseas and need everything handy at any given time or if you live in a remote area where you either can't get to the library easily or you plan on being snowbound for a few months.
I personally put together several things to form my curriculum. I start by going to the North Carolina Department of Public Instruction Website and looking at what the state has the other kids doing in that particular grade level. I actually print it out and as we cover the topics, I check them off in red ink so I can have the visual of 'complete.' Anyway, the only real curriculum items I purchase are math and learning to read materials. Things to complete Science and Social Studies are easily found at even small libraries, and literature is probably either in your home already, at the library, or in the thrift store. I do Handwriting and Grammar at the same time through copywork. I read my son the sentence, have him look at the words and we work on pronounciation, then I write it on writing paper and skip lines so he can copy it on the line directly below. We talk about how words are spelled and what types of punctuation are used and why. a Kindergarten doesn't need to diagram sentences, but when we get there, we can do it the same way. Plus, he gets practice writing lots of different letters instead of a boring page of nothing but the letter p which would bore both me and him stiff in about 10 seconds. I would rather kill 2 or 3 birds with the one stone and one time frame and move on. Plus copy work helps with retention.
Anyway, everyone has their own particular style of homeschooling, but just because someone tells you to 'buy this because it's the best,' don't jump into it, just wait and look around. Best for their kid is not necessarily best for yours!