please do not make your own sunscreen! It is a dangerous thing to try because you have no guarantee that it will protect your skin, and this can lead to badness in the future. I will write more on this topic in the next few days, but I really want to discourage you from this process. Please do not make your own sunscreen!
Will and Patrick's comments and quest for an inexpensive lotion got me thinking about making lotions on a budget. Yes, I have a workshop filled with exotic oils and more spendy ones, and I realize I'm an enabler to the point where your credit card companies and suppliers love me and your partners, spouses, and children hate me, but that's because I want to experiment and share my findings with you, my wonderful readers.
You don't need to have a full complement of every oil your supplier carries to make awesome products! I'd suggest having a very light, light, and medium weight oil along with cocoa butter and another butter in your workshop. Your choice of oils will depend upon the application - are you making lotions and balms or do you want something good for hair as well? - and your preferred skin feel. But for the most part, having four oils and a butter will get you started.
I think fractionated coconut oil is awesome and I suggest it for everyone. It's very light, it's odour free, and it is non-comedogenic, so it's great for pretty much every application. Products made with fractionated coconut oil can be considered "oil free" as it's really more of an ester than an oil, and it's not very greasy. It's not terribly expensive, and I find it use it in many of my products. Plus, with a two year shelf life, you can buy a litre of it and know you'll definitely use it in time!
For the light oils, I always suggest soy bean oil first. It's lightweight, contains a ton of phytosterols and Vitamin E, very moisturizing, and it contains a lot of linoleic acid, which is great for speeding up skin's barrier repair mechanisms. It's really inexpensive - probably the least expensive of all the oils - but it is greasy feeling.
hazelnut or macadamia nut would be my first choices (grapeseed oil's shelf life is far too short to be one of your main oils!). Macadamia nut doesn't have that lovely linoleic acid, but it does have a ton of oleic acid, which is great for moisturizing your skin, and it has quite a lot of phytosterols. Hazelnut oil has more linoleic acid, more Vitamin E, and about the same level of phytosterols as macadamia nut oil, and it's about the same price.
Sweet almond oil and apricot kernel oil have less linoleic acid than soybean oil, but they are both considered light and drier than soybean or sunflower oil. If I had to choose between these two, I'd go with apricot kernel oil as it has higher levels of Vitamin E and phytosterols.
For a medium weight oil, I like rice bran or sesame seed oils. Both are well balanced in linoleic and oleic acids, both contain a ton of phytosterols and Vitamin E, and both are inexpensive. They are considered to be more greasy than something like avocado oil (which is considered astringent and heavy) but on par with olive oil (which is considered medium-heavy). All of these oils are considered inexpensive.
For your butters, I consider cocoa butter a staple as it's inexpensive and is approved by the FDA as a barrier ingredient. If you want to make lotions for the winter, I consider this ingredient almost essential. Mango butter is a good choice if you like drier feeling products; shea butter if you don't mind a little greasiness. The more refined the butter, the less likely you are to find grains in your products.
coconut oil? Coconut oil is a great choice as it's fantastic for hair care products, is less greasy feeling thanks to the tannins, and is really inexpensive. For some reason, I don't use it a lot, I think it's because it's a drier feeling oil and doesn't thicken as well as the butters, but it's a great choice for products, especially if you're budget conscious!
As for exotic oils, well, there's no saving money there! All but a few cost a lot more than our carrier oils, and it's really about what you want in an oil. Click here for the posts on exotic oils (scroll down a bit).