I started with the Cuisinart Blender that we had purchased at Costco several years ago to make baby food for around $80. I know others that have been making them with even cheaper blenders that they've picked up from Walmart, Target or other large department stores.
After you've become addicted to these green smoothies you may want to upgrade. My husband, who is one of the most frugal persons I know, bought me a Vita-Mix for my birthday back in November. Its by far, the best investment we've made for our health yet. A lot of people balk at the idea of spending $400 on a blender, but seriously, I've used it everyday (usually twice) since we purchased it. If you are serious about getting healthy and serious about green smoothies, its a purchase that you will not regret.
A blender, a cutting board and a sharp knife are really all you need to get started. But there are a few other things I have around the house that do make smoothies a little easier and healthier. I picked up a cheap-o citrus juicer at Walmart to juice my own oranges, limes & lemons when I can find them on sale. I'm not a big fan of pulp and while I realize that just tossing the whole fruit in my blender is best, I enjoy juicing them and just using the juice. When I juice the fruits myself I know the juice is fresh, raw and unprocessed. Nut milk bags are another thing that I have in my kitchen. I haven't used them yet, as I just picked them up last week, but I look forward to making some yummy, creamy smoothies with a nut milk base.
There are other tools that raw foodists rave about, but right now I'm only concentrating on my green smoothie habit so this is it for me. Easy peasy. Be sure to stop back on Friday, that's when my smoothie challenge begins!