That's a hard one, you can spend as little or as much as you want really but I do find if you buy a pack that has a lot of similar papers you may get bored.
I would start with something very small and simple just to get you going, you will soon find yourself adding additional bits and pieces to the cards and soon you will know what you enjoy doing and can purchase additional items.
Try experimenting with different techniques and don't be disheartened if they don't turn out perfect most techniques such as embossing and rubber stamping improve the more you practise.
If you get stuck you can post a question here and we will be happy to help
I joined the cardmaker kit-of-the-month club. Every month they send you a new pack of stuff you get enough to make at least 10 cards or more in some cases. you get Paper, cardstock already shaped and scored, embellishments and envelopes, all you need to bring is the glue and your imagination. They also come with a handy idea guide incase you are stuck. I like making my own but if I have no ideas I come to vickis but if you just need a quick cute card this is the way to go. They have a website through cardmakers magazine you can check out.
Hi I found a good site on the net while I am searching for materials. I think they have complete stuff there for cardmaking supplies and kits. You might want to check it out.