There's a huge variety of brands out there which make natural/organic beauty products, and a huge range of prices. A rough guide to brands:
Super-duper low-priced brands: Sukin (skin care, body care and hair care, Natural Instinct (skin care, body care, hair care, sun care, baby care, and household cleaners)
Affordable brands: The Herb Farm (skin care, body care, hair care, mother and baby care, men's products, room sprays, essential oils, and healing products),Weleda (skin care, hair care, body care, mother and baby care, men's products, oral care, homeopathic ointments, and over-the-counter medications)
Mid-range brands: Living Nature (skin care, hair care, body care, mother and baby care, men's products, and makeup), Trilogy (skin care, hair care and body care), Evolu (skin care and body care)
More expensive brands: Dr Hauschka (skin care, hair care, body care, sun care, and makeup), Ayurda (skin care and hair care)
High-end brands: Aveda (skin care, hair care, body care, men's products, makeup, fragrances, and candles), MV Organic Skincare (skin care and body care)
Tip 2: Shop around
There are a lot of natural beauty brands available at health stores, but also check out pharmacies, supermarkets, gift shops and Farmers stores. Prices vary between stores as well, so if you see something you like, maybe check several stores to see if have it, so you can make sure you get the best deal. Also check out offers like gift with purchase, or buy one get one free. Look out for sales, but make sure you check the expiration dates on the products, because sometimes products which are nearing expiration will be sold at half price.
Tip 3: Make use of loyalty cards
Farmers stocks Giovanni, Trilogy, Natio, Living Nature, Evolu and Dr Hauschka. Any purchase from the beauty department will put points on your beauty club card (1 point per dollar), and after spending $200, you get a $20 voucher. I always use mine to put towards buying Dr Hauschka makeup. Life Pharmacy also has a loyalty card, and they stock Living Nature, Trilogy, Evolu, Antipodes, Comvita Huni, Tebe, Weleda baby products, Made 4 Baby, and Kosmea. Their loyalty card rules are slightly different from Farmers' (see http://www.lifepharmacy.co.nz/ for details), but it's good because anything purchase over $5 you make at their stores (with the exception of prescription medications and discount fragrances) will give you points.
Also, Onecard can be used at Foodtown and Woolworths supermarkets, which stock Skinfood, Pure Innosense, Primal Earth, and the Ecostore baby range. You have to spend, like $2000 before you get a voucher, but if you do your regular grocery shopping there, then you'll probably get points fairly quickly. Also, there are often a lot of discounts available for Onecard cardholders.
In addition to this, some brands have loyalty cards of their own, like the Evolu Eleven-for-ten card, and the Living Nature Truly Natural You card. Trilogy also has one, but it can only be used at Health 2000 stores, whereas the Evolu and Living Nature ones can be used at anywhere which stocks those brands.
Tip 4: Try samples, or buy travel/trial-size packs
Some stores have small samples (I think they're free - probably best to check before taking them though!) of Evolu and Living Nature products. These are a good way to test out the product without actually buying it.
A number of brands offer travel/trial packs. Living Nature has quite a few different ones - check them out at https://www.livingnature.com/catalog/main.cfm?t=c&r=vw&cid=1915. Trilogy has Trilogy Travelers - for $60 you get 50l Cream Cleanser, 50ml Hydrating Mist Toner, 50ml Energising Face Lotion, and 50ml Nourishing Body Lotion. Evolu has a Travel Tower, $39, which contains 10ml Creme Cleanser, 10ml Moisturising Day Cream, 10ml Night Cream, 10ml Soothing Eye Gel, 10ml Purifying Mask, and 10ml Hand+Cuticle Cream. Evolu also has the Travel Valet, $35, which consists of 10ml Refreshing Facial Mist, 20ml Day Cream with SPF15, 20ml Silkening Shampoo, 20ml Invigorating Body Lotion, 10ml Healing Lip Treatment, and a luxury facecloth, all in a zipup pouch.
If you want to try out a more affordable range, The Herb Farm has six different trial size packs. Check them out at http://www.herbfarm.co.nz/index.php?cPath=25_38.
Tip 5: Make your own
I tend to be too lazy to do this, but if you'd like to try making your own beauty products, there are plenty of recipes available at http://www.makeyourowncosmetics.com/. Sometimes this can cost a bit of money if you have to buy ingredients, but there are also things you can do, like using olive oil as a hair treatment, that will save a lot of money.