I would suggest simply pulling a couple cards: one for the pro of the purchase, or why you should buy the item, and then one card for the con of the purchase, or why you should not buy the item. I don't really think a great big reading is necessary to look at whether or not it would be a wise move to buy something specific, especially if you already want it bad enough, you're not going to want to have to look into the seriousness of a simple purchase. Ooh, and maybe after pulling the 2 cards, you could pull a central card to be the deciding factor or "most important factor," or something along those lines. If you are in fact going to keep it a simple draw, and if you do read them, I would suggest pulling from the Lenormand for this one. They are a lot more straightforward and are perfect for looking at more superficial matters like this one. All food for thought, though.
I say if you feel the pull toward the item, and you can realistically afford it, then by all means go ahead and get it!